Purification process for hexafluoroethane products

ABSTRACT

The disclosure relates to removing impurities from hexafluoroethane (CF 3  CF 3 ), also known as Perfluorocarbon 116 (PFC-116) or Fluorocarbon 116 (FC-116), by using azeotropic distillation such that an overhead product consisting essentially of HCl-hexafluoroethane is formed, optionally combined with a phase separation step to break the HCl-hexafluoroethane azeotropic or azeotrope-like composition thereby permitting recovery of substantially pure hexafluoroethane. Unreacted hydrogen fluoride (HF) may be removed from hexafluoroethane during the above azeotropic distillation with HCl or alternatively by an azeotropic distillation wherein an HF-hexafluoroethane azeotropic or azeotrope-like composition exits overhead and substantially pure HF exits in the bottoms stream.

This is a continuation of application Ser. No. 08/455,883 filed May 31,1995, now abandoned which is a continuation of application Ser. No.08/309,367, filed Sep. 20, 1994 (pending).

FIELD OF THE INVENTION

The instant invention relates to the field of removing impurities fromhexafluoroethane (CF₃ CF₃), also known as Perfluorocarbon 116 (PFC-116)or Fluorocarbon 116 (FC-116), by using azeotropic distillation such thatan overhead product consisting essentially of HCl-hexafluoroethane isformed, optionally combined with a phase separation step to break theHCl-hexafluoroethane azeotropic or azeotrope-like composition therebypermitting recovery of substantially pure hexafluoroethane. Unreactedhydrogen fluoride (HF) may be removed from hexafluoroethane during theabove azeotropic distillation with HCl or alternatively by an azeotropicdistillation wherein an HF-hexafluoroethane azeotropic or azeotrope-likecomposition exits overhead and substantially pure HF exits in thebottoms stream.

BACKGROUND OF THE INVENTION

Conventional methods for manufacturing hexafluoroethane typically resultin undesired impurities. Hexafluoroethane can be manufactured byfluorinating at least one of trichlorotrifluoroethane,dichlorotetrafluoroethane and/or chloropentafluoroethane. Thishexafluoroethane manufacturing method often produces a product streamcontaining significant amounts of fluorocarbon and acid impurities whichare difficult to remove by conventional distillation techniques.

Various gaseous fluorine-containing compounds are utilized to plasmaetch silicon-type materials in order to fabricate semiconductor devices,e.g., A. J. Woytek, J. Fluor. Chem. 33, 331-334 (1986); the disclosureof which is hereby incorporated by reference. A major use ofhexafluoroethane is as a plasma etchant in semiconductor devicefabrication. It interacts with the surface of the integrated circuitwafer, modifying it so as to lay down the electrical pathways andproviding for the surface functionalities that define the integratedcircuit. As manufacturers are continually trying to increase the numberof functionalities packed per unit surface area, the increasing finenessof surface detail in turn requires greater precision and consistency ofthe effect the etchant has on the wafer substrate. Products of highpurity are critical for this application. It has been found that evenvery small amounts of impurities can result in wide line width and thusless information bits per chip. Moreover, the presence of theseimpurities, including but not limited to particulates, metals, moisture,and other halocarbons in the plasma etchant, even when present only inthe part per million level, increases the defect rate in the productionof these higher density integrated circuits. As a result there has beencontinually increasing market demand for higher and higher purityetchants, and an increasing market value for materials having therequired purity. Consequently, identification of the offendingimpurities and their removal represents a significant aspect ofpreparing the fluorine-containing compounds for these applications.

CROSS-REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS

Certain aspects of this invention are related to the disclosure ofcommonly assigned U.S. patent application Ser. Nos. 08/055,486,08/208,256 and U.S. Pat. No. 5,258,561, (corresponding to EuropeanPatent Application PCT/US94/04301); the entire disclosure of which ishereby incorporated by reference.

SUMMARY OF THE INVENTION

The instant invention solves the problems associated with conventionalhexafluoroethane (FC-116) manufacturing methods by providing anazeotropic distillation method for purifying FC-116. As a result, theinstant invention provides a high purity FC-116 product that is neededas an etchant in the electronics industry.

In one aspect of the invention, we have found that at least one ofchlorotrifluoromethane (CFC-13), trifluoromethane (HFC-23),chlorodifluoromethane (HCFC-22), chloropentafluoroethane (CFC-115),pentafluoroethane (HFC-125), difluoromethane (HFC-32),1,1,1-trifluoroethane (HFC-143a), 1,1-difluoroethane (HFC-152a), and HF,among others, can be removed from hexafluoroethane by being distilled inthe presence of anhydrous HCl; usually, in the presence of an amount ofHCl that is sufficient to form an azeotropic or azeotrope-likecomposition with all of the hexafluoroethane. The instant inventionprovides a process whereby an HCl-hexafluoroethane azeotropic orazeotrope-like composition, which is substantially free of impuritiessuch as chlorotrifluoromethane, trifluoromethane, chlorodifluoromethane,chloropentafluoroethane, pentafluoroethane, difluoromethane,1,1,1-trifluoroethane, 1,1-difluoroethane and HF, can be removed as theoverhead stream from a distillation column. By "substantially free" ofimpurities or "substantially pure", it is meant that the stream containsless than about 1.0 wt %, normally less than 0.1 wt %, and most oftenless than about 10 ppm of undesired impurities, e.g., the instantinvention can produce at least about 99.9999 wt % pure PFC-116. Theseimpurities and/or their azeotropes with HCl or HF can be removed fromthe bottom of the distillation column. This invention can consequentlyproduce PFC-116 that is greater than 99.999% wt. PFC-116 based on theweight of all components contained within, e.g., 99.9999 wt % purePFC-116 or containing less than about 1 ppm of undesired impurities.

Another aspect of the invention provides a process for breaking theHCl-hexafluoroethane azeotropic or azeotrope-like compositions intotheir individual components by liquefying and cooling the recoveredazeotrope composition, and allowing the cooled composition to separateinto HCl-rich and hexafluoroethane-rich layers within a decanter. Thelatter layer may then be purified by, for example, by azeotropicdistillation thereby yielding substantially pure hexafluoroethane.Optionally, the HCl-rich layer may be purified, for example, byazeotropic distillation to produce substantially pure anhydrous HCl.

In another aspect, the invention comprises i) removing a portion of thetrifluoromethane (HFC-23) along with the HCl-hexafluoroethane azeotropicor azeotrope-like composition from a first column's overhead streamwherein the remainder of the HFC-23 (with the other impurities) exits inthe column's bottom stream, ii), separating the overhead stream within adecanter into HCl-rich and hexafluoroethane-rich layers as previouslydescribed, and iii) distilling the hexafluoroethane-rich layer in asecond distillation column and recycling a HCl-hexafluoroethaneazeotrope composition, which exits from the second distillation columnand now contains a portion of the original trifluoromethane, to thefirst distillation column. The hexafluoroethane exiting from the bottomsof the second distillation column will now be substantially free oftrifluoromethane and HCl as well as the other impurities.

In another case, the hexafluoroethane may contain quantities of HCl andoptionally at least one of CFC-13, CFC-115, HFC-23, among others. Byoperating a distillation column under conditions that cause formation ofazeotropic or azeotrope-like compositions consisting essentially of HCland one or more of PFC-116, CFC-13, CFC-115 and HFC-23, suchcompositions can be removed from the distillation column as an overheadproduct thereby purifying the hexafluoroethane. The hexafluoroethanecan, if desired, be purified further by using the aforementionedmethods.

In another case, the hexafluoroethane may contain quantities of HF andoptionally one or more of CFC-115, CFC-114, CFC-114a, CFC-113, CFC-113a,CFC-13, HCFC-22, HFC-143a, HFC-125 among Others. By operating adistillation column under conditions that cause formation of azeotropicor azeotrope-like composition consisting essentially of HF and one ormore of PFC-116, CFC-115, CFC-114, CFC-114a, CFC-113, CFC-113a, CFC-13,HCFC-22, HFC-143a and HFC-125, such azeotropes can be removed therebypurifying the hexafluoroethane. The hexafluoroethane can, if desired, bepurified further by using the aforementioned methods.

In still another case, the hexafluoroethane may contain quantities of atleast one of HFC-23, CFC-13, among others. By operating a distillationcolumn under conditions that cause formation of azeotropic orazeotrope-like compositions consisting essentially of FC-116 and one ormore of HFC-23 and CFC-13, such azeotropes can be removed as an overheadproduct thereby purifying the hexafluoroethane. The remaininghexafluoroethane can, if desired, be purified by using theaforementioned methods.

In a further aspect, the invention can provide an improved process forproducing hexafluoroethane by fluorinating trichlorotrifluoroethane(s),dichlorotetrafluoroethane(s) and/or chloropentafluoroethane to produce ahexafluoroethane product stream containing chlorotrifluoromethane andother fluorocarbon impurities. The improved process comprises the stepsof removing these impurities from the hexafluoroethane product stream byusing the azeotropic distillation processes described above.

The invention also provides a method for separating HF from a mixturecomprising HF and hexafluoroethane wherein the HF is present in excessof the HF-hexafluoroethane azeotropic or azeotrope-like composition. TheHF is separated by removing the HF-hexafluoroethane composition as anoverhead product in a distillation column thereby leaving a purified HFin the bottoms. Further, the invention provides a method for separatinga purified HF from a mixture comprising HF and a number of otherhalogenated compounds, e.g., halocarbons, wherein the HF is present inexcess of the HF-halocarbon azeotropic or azeotrope-like composition. Inthis case, the purified HF is obtained by removing the previouslydescribed HF-halocarbon(s) azeotropic or azeotrope-like mixtures as anoverhead from a distillation column thereby leaving purified HF in thebottoms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1--FIG. 1 is a schematic diagram of a process that can be used forpracticing the inventive process.

FIG. 2--FIG. 2 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of HCl and PFC-116 ata temperature of about -20.56 deg C.

FIG. 3--FIG. 3 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of HCl and CFC-13 ata temperature of about -20 deg C.

FIG. 4--FIG. 4 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of HCl and HFC-23 ata temperature of about -20 deg C.

FIG. 5--FIG. 5 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of HCl and CFC-115 ata temperature of about -30 deg C.

FIG. 6--FIG. 6 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of PFC-116 and HF ata temperature of about -20 deg C.

FIG. 7--FIG. 7 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of CFC-13 and PFC-116at a temperature of about -45.55 deg C.

FIG. 8--FIG. 8 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of HFC-23 and PFC-116at a temperature of about -45.55 deg C.

FIG. 9--FIG. 9 is a graphical representation of azeotropic andazeotrope-like compositions consisting essentially of PFC-116 and HFC-32at a temperature of about -19.6 deg C.

FIG. 10--FIG. 10 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of CFC-115 and HF ata temperature of about -20 deg C.

FIG. 11--FIG. 11 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of CFC-114 and HF ata temperature of about -20 deg C.

FIG. 12--FIG. 12 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of CFC-114a and HF ata temperature of about 20 deg C.

FIG. 13--FIG. 13 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of CFC-113 and HF ata temperature of about -20 deg C.

FIG. 14--FIG. 14 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of CFC-113a and HF ata temperature of about 20 deg C.

FIG. 15--FIG. 15 is a graphical representation of an azeotropic andazeotrope-like compositions consisting essentially of HFC-125 and HF ata temperature of about 20 deg C.

FIG. 16--FIG. 16 is a graphic representation of azeotropic andazeotrope-like compositions consisting essentially of CFC-13 and HF at atemperature of about -20 deg C.

FIG. 17--FIG. 17 is a graphic representation of azeotropic andazeotrope-like compositions consisting essentially of HCFC-22 and HF ata temperature of about 70 deg C.

FIG. 18--FIG. 18 is a graphic representation of azeotropic andazeotrope-like compositions consisting essentially of HFC-143a and HF ata temperature of about 30 deg C.

DETAILED DESCRIPTION

The present invention relates to a method for purifying hexafluoroethaneproducts containing one or more impurities such aschlorotrifluoromethane, trifluoromethane, chlorodifluoromethane,chloropentafluoroethane, difluoromethane, 1,1,1-trifluoroethane,1,1-difluoroethane, pentafluoroethane, among others. The presentinvention also relates to a method for removing acids such as hydrogenfluoride and/or hydrogen chloride, that may be present in thehexafluoroethane, e.g., at least one of hydrogen fluoride and hydrogenchloride that may be present in the hexafluoroethane as a residualreactant or reaction product.

An aspect of the inventive process comprises operating a conventionaldistillation column under conditions sufficient to form aHCl-hexafluoroethane azeotropic or azeotrope-like composition whereinthe composition is substantially free of at least one of the followingimpurities: chlorotrifluoromethane, trifluoromethane,chlorodifluoromethane, difluoromethane, chloropentafluoroethane,pentafluoroethane, 1,1,1-trifluoroethane, 1,1-difluoroethane, HF, amongothers. The HCl-hexafluoroethane azeotropic or azeotrope-likecomposition can be removed as an overhead stream from the top of thedistillation column, and the previously identified impurities or theirazeotropes with HCl and/or HF can be removed from the bottom of thedistillation column.

Another aspect of the invention relates to an optional process forseparating an HCl-hexafluoroethane azeotropic or azeotrope-likecomposition, e.g., the previously discussed azeotropic composition beingrecovered as an overhead stream, into its individual components. Theazeotropic or azeotrope-like composition can be separated into itscomponents by cooling and liquefying the azeotropic composition to belowabout -50 degrees C. within a conventional decanter thereby allowing thecomposition to separate into HCl-rich and hexafluoroethane-rich layers.

The hexafluoroethane-rich layer may then be purified by azeotropicdistillation in a second distillation column, wherein any remaining HClcan be removed as the HCl-hexafluoroethane azeotropic or azeotrope-likecomposition in an overhead stream from the top of the seconddistillation column thereby yielding substantially pure hexafluoroethanefrom the bottom of the second column. In other words, the relativelysmall mount of HCl is removed from the hexafluoroethane-rich layer byremoving substantially all of the HCl and a portion of thehexafluoroethane as an azeotropic or azeotrope-like composition. Theremaining hexafluoroethane is substantially pure.

The HCl-rich layer may then also be purified by azeotropic distillationin a third distillation column, wherein any remaining hexafluoroethanecan be removed as the HCl-hexafluoroethane azeotropic or azeotrope-likecomposition in an overhead stream from the top of the third distillationcolumn thereby yielding substantially pure HCl from the bottom of thethird column. In other words, the relatively small amount ofhexafluoroethane is removed from the HCl-rich layer by removingsubstantially all of the hexafluoroethane and a portion of the HCl as anazeotropic or azeotrope-like composition. The remaining HCl issubstantially pure.

The instant invention also provides a method for removing certainquantities of trifluoromethane (HFC-23) along with theHCl-hexafluoroethane azeotropic or azeotrope-like composition as anoverhead stream in the first distillation column. Any remainingtrifluoromethane can be removed with the other impurities in the firstcolumn's bottom stream. The overhead product stream can be separated bybeing introduced into a decanter that causes formation of HCl-rich andhexafluoroethane-rich layers wherein the hexafluoroethane-rich layerincludes the portion of trifluoromethane that exited the top of thecolumn. The hexafluoroethane-rich layer can be removed from the decanterand introduced into a second distillation column wherein the overheadproduct stream contains the HCl-hexafluoroethane azeotropic orazeotrope-like composition and trifluoromethane; both of which can berecycled to the first distillation column. Hexafluoroethane exits fromthe bottoms of the second distillation column and is normallysubstantially free of trifluoromethane as well as the impurities thatwere removed by the first distillation column.

The hexafluoroethane product or feedstock to be purified by this processtypically has at least about 90 organic mole percent hexafluoroethane,usually has at least 95 organic mole percent hexafluoroethane, andnormally has at least about 99 organic mole percent hexafluoroethane.

The previously described processes can be employed by using anHF-hexafluoroethane azeotropic distillation process. TheHF-hexafluoroethane azeotropic distillation process can be employedbefore, after and/or in some cases as a replacement for theHCl-hexafluoroethane azeotropic distillation process.

Hexafluoroethane products or feedstocks that can be purified bypracticing the instant invention may be obtained from any suitablesource. One suitable source is a process comprising reacting anhydroushydrogen fluoride with any one of 1,1,1-trichloro-2,2,2-trifluoroethane(CFC-113a), 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113),1,1-dichloro-1,2,2,2-tetrafluoroethane (CFC-114a) or1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114), to formchloropentafluoroethane (CFC-115) and hexafluoroethane (PFC-116), amongother compounds. Examples of a suitable process is described inHeterogeneous Catalytic Reactions of Chlorofluoro-Carbons. Blanchard,M.; Wendlinger, L. Canesson, P. Appl. Catal.(1990), 59 (1), 123-8, thedisclosure of which is hereby incorporated by reference.

Any unreacted starting materials and CFC-115 may be recycled to thereactor to produce additional quantities of PFC-116. Impurities such aschlorotrifluoromethane (CFC-13), trifluoromethane (HFC-23),chlorodifluoromethane (HCFC-22), difluoromethane (HFC-32),chloropentafluoroethane (CFC-115), 1,1,1-trifluoroethane (HFC-143a),1,1-difluoroethane (HFC-152a), pentafluoroethane (HFC-125) as well asunreacted HF and byproduct HCl may also be present in thehexafluoroethane product.

Conventional distillation can be used in order to remove a portion ofthe impurities such as hydrogen chloride, hydrogen fluoride andhigh-boilers including tars, to produce a hexafluoroethane product whichcontains at least about 90 organic mol percent hexafluoroethane.

If desired, bulk quantities of impurities in the hexafluoroethaneproduct can also be removed from the hexafluoroethane product by usingazeotropic distillation. For example, the impurity concentration can bereduced by passing the hexafluoroethane containing product through adistillation column which is operated under conditions sufficient topermit withdrawing at least one of following azeotropic orazeotrope-like compositions as an overhead product: HCl/PFC-116,HCl/CFC-13, HCl/HFC-23, HCl/CFC-115, PFC-116/HFC-23, PFC-116/CFC-13,PFC-116/HFC-32, HF/PFC-116, HF/CFC-115, HF/CFC-114. HF/CFC-114a,HF/CFC-113, HF/CFC-113a, HF/CFC-13, HF/HCFC-22, HF/HFC-143a, HF/HFC-125,among others. The previously described HCl-hexafluoroethane and/orHF-hexafluoroethane azeotropic distillation processes can then beemployed to produce substantially pure hexafluoroethane.

A key aspect of this invention relates to the relative volatilities ofhexafluoroethane and each of its impurities versus anhydrous HCl, and toa lesser extent to the relative volatility of hexafluoroethane versusHF. To determine the relative volatility of hexafluoroethane and HCl,for example, the so-called PTx Method was used. In this procedure, thetotal absolute pressure in a cell of known volume is measured at aconstant temperature for various known binary compositions. Use of thePTx Method is described in greater detail in "Phase Equilibrium inProcess Design", Wiley-Interscience Publisher, 1970, written by HaroldR. Null, on pages 124 to 126; the entire disclosure of which is herebyincorporated by reference.

These measurements can reduced to equilibrium vapor and liquidcompositions in the PTx cell by an activity coefficient equation model,such as the Non-Random, Two-Liquid (NRTL) equation, to represent liquidphase non-idealities. Use of an activity coefficient equation, such asthe NRTL equation, is described in greater detail in "The Properties ofGases and Liquids", 4th edition, publisher McGraw Hill, written by Reid,Prausnitz and Poling, on pages 241 to 387; and in "Phase Equilibria inChemical Engineering, published by Butterworth Publishers, 1985, writtenby Stanley M. Walas, pages 165 to 244; the entire disclosure of which ishereby incorporated for reference.

The behavior of hydrogen fluoride in such systems may also be calculatedby using an appropriate hydrogen fluoride association model inconjunction with the aforementioned methods as described by W. Schotte,Ind. Eng. Chem. Process Des. Dev. 1980, 19, pp 432-439; the entiredisclosure of which is hereby incorporated by reference.

Without wishing to be bound by any theory or explanation, it is believedthat the NRTL equation in conjunction with the other referenced modelscan sufficiently predict whether or not hexafluoroethane and HClmixtures and/or the following other mixtures behave in an ideal manner,and can sufficiently predict the relative volatilities of the componentsin such mixtures.

The results of PTx measurements and the above series of calculations aresummarized in Tables 1 and 2 below, giving results for mixturesconsisting essentially of PFC-116 with CFC-13 at about -18.55 degrees C.and PFC-116 with HFC-23 at about -45.55 degrees C. respectively.

                  TABLE 1                                                         ______________________________________                                        Vapor-Liquid Measurements on PFC-116/CFC-13 System                            at -18.55 Deg C.                                                              Mole % PFC-116                                                                          Pressure Activity Coefficient                                                                       Relative Volatility                           Liquid                                                                              Vapor   psia     PFC-116                                                                              CFC-13                                                                              PFC-116/CFC-13                            ______________________________________                                        0.00  0.00    170.84   1.191  1.000 1.091                                     3.78  4.06    171.58   1.174  1.000 1.077                                     9.44  9.92    172.38   1.149  1.002 1.057                                     15.07 15.55   173.02   1.127  1.004 1.038                                     19.97 20.32   173.34   1.110  1.008 1.022                                     25.04 25.16   173.55   1.095  1.012 1.006                                     32.43 32.09   173.37   1.074  1.019 0.985                                     47.97 46.50   172.27   1.041  1.041 0.943                                     57.68 55.60   170.74   1.026  1.058 0.919                                     62.83 60.52   169.53   1.019  1.068 0.907                                     69.05 66.59   168.12   1.013  1.081 0.893                                     74.69 72.23   166.45   1.008  1.094 0.881                                     89.24 87.62   161.62   1.001  1.131 0.853                                     94.78 93.87   159.48   1.000  1.146 0.843                                     100.00                                                                              100.00  157.25   1.000  1.161 0.834                                     ______________________________________                                    

The "Mole %" column refers to the quantity of PFC-116 that is in theliquid and vapor portions of the PFC-116/CFC-13 mixture within the PTxCell.

                  TABLE 2                                                         ______________________________________                                        Vapor-Liquid Measurements on PFC-116/HFC-23 System                            at -45.55 Deg C.                                                              Mole % PFC-116                                                                          Pressure Activity Coefficient                                                                       Relative Volatility                           Liquid                                                                              Vapor   psia     PFC-116                                                                              HFC-23                                                                              PFC-116/HFC-23                            ______________________________________                                        0.00  0.00    83.91    3.047  1.000 2.394                                     8.25  15.18   92.69    2.523  1.008 1.992                                     15.73 23.95   97.84    2.164  1.029 1.687                                     21.62 29.01   99.82    1.940  1.055 1.482                                     30.92 35.13   101.62   1.664  1.115 1.210                                     46.70 43.04   102.62   1.348  1.273 0.862                                     50.52 44.81   102.14   1.292  1.325 0.795                                     71.32 56.11   95.77    1.089  1.731 0.514                                     73.92 57.99   93.89    1.073  1.800 0.487                                     78.66 61.91   90.94    1.048  1.940 0.441                                     85.16 68.84   85.59    1.023  2.167 0.385                                     86.73 70.88   84.49    1.018  2.228 0.372                                     92.08 79.46   77.59    1.006  2.460 0.333                                     96.04 88.11   71.99    1.002  2.656 0.306                                     100.00                                                                              100.00  64.64    1.000  2.879 0.281                                     ______________________________________                                    

The "Mole %" column refers to the quantity of PFC-116 that is in theliquid and vapor portions of the PFC-116/HFC-23 mixture within the PTxCell.

In Tables 1 and 2 above, the "Relative Volatility" column shows thoserelative volatilities calculated by using PTx cell pressure which wasmeasured at the temperature indicated on the above Tables. While therelative volatility of PFC-116 in comparison to CFC-13 or HFC-23 atrelatively low concentrations is sufficient to permit separating thePFC-116 by conventional methods, the relative volatility becomes 1.0 as29 mole % PFC-116 is approached at -18.55 degrees C. in the 116/13 case,and becomes 1.0 as 40.0 mole % PFC-116 is approached at -45.55 degreesC. in the 116/23 case. Relative volatilities of 1.0 indicate thepresence of an azeotropic or azeotrope-like composition, that rendersseparating the components of such compositions impractical by usingconventional distillation, or necessitates employing an extremely largeand expensive distillation column for their separation. The presence ofan azeotropic or azeotrope-like composition will also be indicatedwhere, at a given temperature, the PTx cell pressure of specificcompositions of mixture of the components is greater than the pressureof other compositions of the same components and of the individualcomponents by themselves, where the azeotropic or azeotrope-likecomposition is that of the cell vapor space in the maximum pressureregion.

Similar to the above examples and discussion, azeotropic orazeotrope-like compositions have been discovered between PFC-116 andrelatively small amounts of certain halocarbon impurities, e.g., PFC-116and HFC-32. Vapor-liquid equilibrium tangent pinches have beendiscovered between PFC-116 and relatively small amounts of certain otherhalocarbon impurities, e.g., PFC-116 and HFC-143a, and PFC-116 andHFC-152a. The presence of such impurities in the PFC-116 product arebarriers to obtaining substantially pure PFC-116 in high yield.

We have similarly found that azeotropic or azeotrope-like compositionsexist between PFC-116 and HCl at a variety of temperatures andpressures. The result of PTx measurements and the above series ofcalculations for mixtures of PFC-116, CFC-13 and HFC-23 with HCl atabout -20 degrees C. are summarized in Tables 3 through 5.

                  TABLE 3                                                         ______________________________________                                        Vapor-Liquid Measurements on HCl/PFC-116 Binary Mixture                       at -20.56 Degrees C.                                                          Mole % HCl                                                                              Pressure Activity Coefficient                                                                       Relative Volatility                           Liquid                                                                              Vapor   psia     HCl   PFC-116                                                                              PFC-116/HCl                               ______________________________________                                        100.00                                                                              100.00  211.3    1.000 14.019 8.74                                      91.92 70.20   298.6    1.030 6.616  4.83                                      72.61 63.65   318.0    1.266 2.395  1.514                                     58.82 62.41   319.1    1.539 1.638  0.860                                     44.07 59.07   311.7    1.937 1.281  0.546                                     26.78 50.52   284.7    2.602 1.087  0.358                                     4.16  16.33   181.7    4.045 1.002  0.222                                     0.00  0.00    149.9    4.428 1.000  0.204                                     ______________________________________                                    

The "Mole %" column refers to the quantity of HCl that is in the liquidand vapor portions of the HCl/PFC-116 mixture within the PTx Cell.

Table 3 shows the presence of an HCl/PFC-116 azeotropic compositionconsisting essentially of about 62% HCl and 38% PFC-116 at -20.56degrees C., with a vapor pressure of about 319 psia.

                  TABLE 4                                                         ______________________________________                                        Vapor-Liquid Measurements on HCl/CFC-13 Binary Mixture                        at -20 Degrees C.                                                             Mole % HCl                                                                              Pressure Activity Coefficient                                                                       Relative Volatility                           Liquid                                                                              Vapor   psia     HCl   CFC-13 HCl/CFC-13                                ______________________________________                                        100.00                                                                              100.00  215.15   1.000 5.152  0.291                                     92.33 82.39   250.10   1.014 3.632  0.389                                     78.79 69.80   271.40   1.094 2.290  0.622                                     69.81 65.47   276.28   1.182 1.830  0.820                                     61.32 62.18   277.29   1.289 1.550  1.037                                     50.00 57.77   274.80   1.472 1.311  1.368                                     35.83 50.70   263.18   1.777 1.137  1.842                                     8.52  21.33   201.93   2.698 1.007  2.912                                     0.00  0.00    164.41   3.117 1.000  3.285                                     ______________________________________                                    

The "Mole %" column refers to the quantity of HCl that is in the liquidand vapor portions of the HCl/CFC-13 mixture within the PTx Cell.

Table 4 shows the presence of an HCl/CFC-13 azeotropic compositionconsisting essentially of about 62% HCl and 38% CFC-13 at -20 degreesC., with a vapor pressure of about 277 psia.

                  TABLE 5                                                         ______________________________________                                        Vapor-Liquid Measurements on the HCl/HFC-23 Binary Mixture                    at -20 Degrees C.                                                             Mole % HCl                                                                              Pressure Activity Coefficient                                                                       Relative Volatility                           Liquid                                                                              Vapor   psia     HCl   HFC-23 HFC-23/HCl                                ______________________________________                                        100.00                                                                              100.00  215.47   1.000 2.671  2.321                                     90.05 83.12   241.00   1.013 2.073  1.838                                     71.91 66.78   259.26   1.093 1.491  1.274                                     65.75 62.68   262.28   1.134 1.375  1.143                                     60.99 59.66   263.29   1.170 1.302  1.057                                     56.57 56.90   263.29   1.207 1.246  0.987                                     52.33 54.22   262.58   1.245 1.200  0.927                                     29.30 37.39   250.32   1.506 1.050  0.694                                     8.84  14.56   221.34   1.812 1.004  0.569                                     0.00  0.00    202.23   1.968 1.000  0.529                                     ______________________________________                                    

The "Mole %" column refers to the quantity of HCl that is in the liquidand vapor portions of the HCl/HFC-23 mixture within the PTx Cell.

Table 5 shows the presence of an HCl/HFC-23 azeotropic compositionconsisting essentially of about 57% HCl and 43% HFC-23 at -20 degreesC., with a vapor pressure of about 263 psia.

Hydrogen fluoride may also be present in the PFC-116 product orfeedstock by virtue of being a residual reactant from the PFC-116manufacturing process. Tables 6 and 7 list vapor-liquid equilibrium datafor PFC-116 with HF and CFC-13 with HF, each pair at a temperature ofabout -20 degrees C.

                  TABLE 6                                                         ______________________________________                                        Vapor-Liquid Measurements on the HF/PFC-116 Binary Mixture                    at -20 Degrees C.                                                             Mole % HF    Pressure    Activity Coefficient                                 Liquid   Vapor   psia        HF    PFC-116                                    ______________________________________                                        100.00   100.00  2.8         1.000 42.16                                      98.73    17.83   54.8        1.002 32.87                                      93.95    8.29    145.1       1.029 15.60                                      92.49    7.96    154.0       1.043 13.04                                      2.37     3.08    152.4       33.44 1.006                                      1.41     1.04    153.3       41.09 1.002                                      0.00     0.00    151.5       57.63 1.000                                      ______________________________________                                    

Table 6 shows the presence of an HF/PFC-116 azeotropic composition at atemperature of about -20 degrees C. with a vapor pressure of about 154psia, as indicated by mixtures of HF and PFC-116 having a higher vaporpressure than either pure component at this temperature, with thecomposition of the vapor in the maximum pressure region being that ofthe azeotrope. Samples of the vapor and NRTL calculations indicate thatthe azeotropic or azeotrope-like composition consists essentially ofabout 5.6 mole % HF and 94.4 mole % PFC-116. It is important to notethat azeotropic and azeotrope-like compositions consisting essentiallyof HF and PFC-116 are found at a variety of temperatures and pressures.For example, at a temperature of about -40 degrees C., the HF/PFC-116azeotrope consists essentially of about 5.4 mole percent HF and 94.6mole percent PFC-116 and a vapor pressure of about 79.6 psia, whereas atabout 0 degrees C., the azeotrope has a composition consistingessentially of about 11 mole percent HF and 89 mole percent PFC-116 anda vapor pressure of about 273 psia. Consequently, operating adistillation column at different temperatures and pressures may altersuch HF/PFC-116 azeotropic or azeotrope-like compositions. Suchazeotropic or azeotrope-like compositions, however, differ only slightlyin composition and vapor pressure from pure PFC-116 thereby rendering itvirtually impossible to recover substantially pure PFC-116 from PFC-116and HF mixtures.

Amounts of HF in excess of the HF/PFC-116 azeotropic composition may bepartially separated from PFC-116/HF mixtures by using a distillationcolumn wherein purified HF exits the bottoms of the distillation column,and the HF/PFC-116 azeotropic or azeotrope-like composition exits thedistillation column as an overhead product. However, in suchcircumstances a method is still required to separate the remaining HFfrom the PFC-116/HF azeotrope.

Other conventional methods for separating HF and PFC-116 are expensiveand impractical. For example, the HF may be removed from PFC-116 bycontacting the PFC-116/HF mixture with water, the HF beingpreferentially absorbed into the water solution typically producing anaqueous HF solution as a by-product.

An azeotropic or azeotrope-like composition can also form between HF andCFC-13. The result of PTx measurements for mixtures of HF and CFC-13 areshown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Vapor-Liquid Measurements on the HF/CFC-13 Binary Mixture                     at -20 Degrees C.                                                             Mole % HF    Pressure    Activity Coefficient                                 Liquid   Vapor   psia        HF    CFC-13                                     ______________________________________                                        100.00   100.00  2.8         1.000 30.73                                      96.75    10.13   96.7        1.007 19.29                                      77.73    5.72    165.0       1.221 4.37                                       75.94    5.74    165.6       1.251 4.04                                       3.68     9.01    166.4       28.11 1.015                                      1.94     2.24    166.3       40.42 1.OO5                                      1.91     2.16    165.7       40.68 1.004                                      0.00     0.00    164.6       65.28 1.000                                      ______________________________________                                    

Table 7 shows the presence of an HF/CFC-13 azeotropic composition at atemperature of about -20 degrees C. with a vapor pressure of about 166psia, as indicated by mixtures of HF and CFC-13 having a higher vaporpressure than either pure component at this temperature, wherein thecomposition of the vapor in the maximum pressure region corresponds tothe azeotrope. Samples of the vapor and NRTL calculations indicate thatthe azeotropic or azeotrope-like composition was about 6.0 mole % HF and94.0 mole % PFC-116 at this temperature.

Similar to the above discussion, azeotropic or azeotrope-likecompositions have been discovered between HF and certain other potentialprocess and product stream components, e.g., HF and CFC-115, HF andCFC-114, HF and CFC-114a, HF and CFC-113, HF and CFC-113a, HF andHCFC-22, HF and HFC-125, HF and HFC-143a, among others.

A comparison of the above azeotropes indicates that the HCl/PFC-116azeotropic or azeotrope-like compositions possess a relatively highervapor pressure, i.e., the azeotropic compositions are more volatile,than any of the previously tabulated azeotropes at a given temperature.For example, FIGS. 2-18, which are discussed below in greater detail,show the variation in vapor pressure as a function of liquid compositionfor various binary mixtures, such as those consisting essentially ofHCl, HF, PFC-116, HFC-23, and CFC-13. These Figures illustrate thesurprising and unexpected differences in vapor pressure found among thePFC-116/HCl azeotropic or azeotrope-like compositions in comparison tothe previously identified impurities and azeotropic or azeotrope-likecompositions thereof. The present invention utilizes these differencesin vapor pressure to purify PFC-116 in an efficient and economicalmanner. Such differences in vapor pressure permit purifying ahexafluoroethane feedstock or product that contains a wide range ofimpurities. Depending upon the characteristics of the azeotropic orazeotrope-like impurity composition, these compositions may be recoveredas a useful product.

For essentially complete recovery of substantially pure PFC-116 from thefeedstock being supplied to the distillation column, the amount of HClin the distillation column should preferably be sufficient to form anazeotropic or azeotrope-like composition with the PFC-116. Given therelatively high volatility of the PFC-116/HCl azeotropic orazeotrope-like compositions, the PFC-116/HCl azeotropes are recoveredfrom the distillation column as an overhead product. If the amount ofHCl is insufficient, the non-azeotroped portion of the PFC-116 may exitthe distillation column either with the overhead stream or the bottomsstream or both, depending upon distillation conditions. If the amount ofHCl present in the distillation column is in excess of the quantitysufficient to form the PFC-116/HCl azeotropes, the excess HCl will exitthe bottom of the column along with other impurities and/or theirazeotropes.

The specific conditions that can be used for practicing of the inventiondepend upon a number of parameters such as the diameter of thedistillation column, the location of feed points, the number ofseparation stages in the column, the reflux ratio used, among otherparameters. In addition to the hexafluoroethane product or feedstock tobe purified, recycle streams from other points in the overallpurification process may be fed to the distillation column, preferablyat a feed point most nearly matching the composition flowing past thatpoint in the column. The operating pressure of the distillation systemmay range from about 15 to 350 psia, normally about 50 to 350 psia.Typically, an increase in the reflux ratio results in an increase in thepurity of the HCl/PFC-116 azeotrope, but generally the reflux ratioranges from 1/1 to about 20/1, normally 5/1 to 10/1. The temperature ofthe condenser, which is located adjacent to the top of the column, isnormally sufficient to substantially fully condense the HCl/PFC-116azeotrope exiting the top of the column, e.g., about -60 deg C. to about10 deg C., at about 80.6 to about 681 psia respectively.

Normally, it is desirable that the HCl/PFC-116 azeotropic orazeotrope-like compositions are separated into their components so thatsubstantially pure anhydrous HCl and PFC-116 can be marketedindividually. While such separation could be achieved by extracting theHCl with water, this would require drying the purified PFC-116 to removeeven traces of water. More importantly, water extraction would generatean aqueous HCl stream which has a lower market value than anhydrous HCl.

We have discovered that HCl/PFC-116 azeotropic or azeotrope-likecompositions may be separated into an acid-rich layer or phase andorganic-rich layer or phase by cooling the compositions within acommercially available decanter to a temperature below about -50 degreesC., with the separation efficiency increasing with lower temperatures.The separated layers can then be decanted. The composition of theacid-rich and organic-rich layers is determined primarily by thetemperature to which the azeotrope composition was cooled.

The effects of temperature upon the azeotrope composition duringdecantation were measured. Azeotropic or azeotrope-like compositions ofHCl and PFC-116 were added to a stirred pressurized cell. The stirringwas then stopped, thereby allowing the mixture to achieve equilibrium ata given temperature. When the mixture had separated into two phases,samples were withdrawn from each separated layer for analysis. Samplesof the vapor space within the pressurized cell were also taken in orderto provide more accurate data, where the vapor space compositionrepresents the azeotrope composition at that temperature. Tests showedsubstantially only a single liquid phase was present at a temperature ofabout -40 degrees C. At about -50 degrees C. and -60 degrees C., twoliquid phases formed, with the results tabulated in Table 8 below.

                  TABLE 8                                                         ______________________________________                                        Vapor-Liquid-Liquid Equilibrium Measurements                                  on the HCl/PFC-116 System                                                                     Mole Fraction of HCl                                                          -50 degrees C.                                                                         -60 degrees C.                                       ______________________________________                                        Lower liquid (PFC-116-rich layer)                                                               0.5080     0.3029                                           Upper liquid (HCl-rich layer)                                                                   0.8929     0.9502                                           Vapor (azeotrope composition)                                                                   0.6182     0.6199                                           Pressure, psia    123.4      83.6                                             ______________________________________                                    

Table 8 shows that there is a substantial difference between thecompositions of the two liquid layers, with the efficiency and degree ofHCl/PFC-116 separation increasing as the temperature is lowered. Inaddition, there is a substantial difference among the composition ofeach of the liquid phases in comparison to the original azeotropiccomposition. The PFC-116-rich liquid layer can be withdrawn from thepressurized cell, which functions as a decanter, and separated furtherby being supplied to a distillation column wherein HCl can be distilledoverhead as HCl/PFC-116 azeotropic or azeotrope-like compositions,leaving substantially pure PFC-116 recovered from the column bottoms.The substantially pure PFC-116 may then be given a final purification toremove trace impurities by being passed through ion exchange beds orother known means to achieve even higher purity. The HCl/PFC-116azeotropic or azeotrope-like compositions distilled overhead may berecycled to either the first distillation column or a decanter.

Similarly, the HCl-rich liquid layer can be withdrawn from thepressurized cell (decanter) and separated further by using adistillation column to distill azeotropic or azeotrope-like HCl/PFC-116compositions overhead thereby leaving substantially pure anhydrous HClrecovered from the column bottoms, e.g., the anhydrous HCl is a valuedproduct for a variety of food and pharmaceutical applications. When HClis present in excess of the amount required to form low boilingazeotropes with organic components, such azeotropes are useful in thatthey can be used for removing the organic components by distilling theHCl/organic azeotropic or azeotrope-like compositions overhead therebyleaving substantially pure HCl. The HCl containing azeotropic orazeotrope-like compositions that can be formed consist essentially ofone or more of the following mixtures: HCl and PFC-116, HCl and CFC-13,HCl and HFC-23, HCl and CFC-115, among others.

In some cases, the HCl-rich layer can alternately be withdrawn from thedecanter and recycled to the first distillation column; e.g., the HClwithin the HCl-rich layer can be employed to form the PFC-116/HClazeotropic or azcotrope-like compositions in the first distillationcolumn. In other words, the acid-rich layer withdrawn from the decanterwould in turn become a component of the azeotropic or azeotrope-likecompositions which are recovered from the first distillation column asan overhead product. Any excess or remaining HCl would exit the bottomof the first column with the organic impurities.

The liquid-liquid decantation temperature is essentially an economicdecision, wherein the higher degree of separation between the PFC-116and HCl which is achieved at increasingly lower temperatures must bebalanced against the higher cost of increasingly lower temperaturerefrigeration.

With respect to a mixture containing HCl, PFC-116, and at least HFC-23,although FIG. 2 and FIG. 4 show a substantial difference among the vaporpressures of the PFC-116/HCl azeotropic or azeotrope-like compositionsand the HFC-23 /HCl azeotrope, further tests have indicated that thisdifference is essentially nullified when the amount of HFC-23 remainingin the PFC-116 product approaches zero because of the activitycoefficients at this low concentration. That is, while it is possible tosomewhat separate the PFC-116/HCl and HFC-23 /HCl azeotropes bydistillation, it is not possible to remove substantially all of theHFC-23 from PFC-116 in a single distillation column. This difficulty canbe overcome by increasing the concentration of HFC-23 by recycling anyHFC-23, which exits the distillation column with the PFC-116, back intothe distillation column until the HFC-23 concentration is sufficient topermit separation by azeotropic distillation. For example, the overheadstream containing the PFC-116/HCl azeotropic or azeotrope-likecompositions, and the remainder of the HFC-23 or azeotropes thereof canbe cooled and fed to a decanter to break the recovered overhead streaminto its individual components, e.g., a PFC-116 rich phase or layer. ThePFC-116-rich phase may then be transported to a second distillationcolumn where the HCl/116 and HCl/23 azeotropes may be distilled overheadthereby producing substantially pure PFC-116 out the column bottoms.This distillate may then be fed back to the first column, therebyproducing the desired effect of increasing the HFC-23 concentration inthat column.

One system that can be used for practicing the instant invention isshown by the schematic diagram in FIG. 1. Referring now to FIG. 1, ahexafluoroethane product or feedstock is supplied by conduit 1containing PFC-116, HCl and at least one member selected from the groupconsisting of chlorotrifluoromethane, trifluoromethane,chlorodifluoromethane, chloropentafluoroethane, pentafluoroethane,1,1,1-trifluoroethane, 1,1-difluoroethane, HF, among others, isintroduced to distillation column 2. An anhydrous HCl product thatcontains other impurities is removed from the bottom of column 2. AnHCl/PFC-116 azeotropic or azeotrope-like composition is removed underreflux from column 2 as an overhead product. At least a portion of theHCl/PFC-116 containing stream can be returned to the top of the columnas condensed reflux. The ratio of condensed material, which is returnedto the column, to the amount of material removed from the column iscommonly referred to as the "reflux ratio". The material exiting the topof the column that is not refluxed may then be transported via conduit 3to a commercially available prechiller 4 that is operated at atemperature of about -50 to -60 deg. C. The chilled composition issupplied to a commercially available decanter 5. The decanter 5 isoperated at a temperature less than -50 deg. C., normally at least -50to -60 deg C., thereby causing the azeotropic composition to beseparated into two liquid layers or phases. The lower layer comprises aPFC-116-rich phase and the top layer comprises a HCl-rich phase. Whilethe top layer is HCl-rich, a relatively small quantity of PFC-116 can bepresent in this layer. The HCl-rich layer is withdrawn from decanter 5and recycled via conduit 6 to column 2. The recycled HCl-rich layerbecomes a source of HCl that is employed to form additional HCl/PFC-116azeotropic or azeotrope-like compositions in column 2. The PFC-116-richlayer is withdrawn from the bottom of decanter 5 and supplied viaconduit 7 to a second distillation column 8. An overhead product streamcontaining the HCl/PFC-116 azeotropic or azeotrope-like composition isremoved, under reflux, from column 8, and recycled via conduit 9 to thefirst distillation column 2. Similar to the HCl/PFC-116 compositionssupplied via conduit 6, the HCl/PFC-116 azeotropic or azeotrope-likecompositions in conduit 9 also becomes a source of HCl to formadditional quantities of the HCl/PFC-116 azeotropic or azeotrope-likecompositions formed in column 2. A substantially pure PFC-116 productexits the bottom 10 of column 8.

While the best results are normally obtained by operating the inventiveprocess under conditions that maximize formation of the HCl/PFC-116azeotropic or azeotrope-like compositions and minimize formation ofhalocarbon/halocarbon azeotropic or azeotrope-like compositions, suchhalocarbon/halocarbon azeotropic or azeotrope-like compositions may beused to purify PFC-116 and/or obtain useful products. In the lattercase, the halocarbon/halocarbon azeotropic or azeotrope likecompositions can be employed as a pre-purification step for removingrelatively large or bulk quantities of impurities from thehexafluoroethane product that in turn can be processed in accordancewith the instant invention. The halocarbon/halocarbon azeotropic orazeotrope-like compositions that can be formed consist essentially ofone or more of the following mixtures: PFC-116 and CFC-13; PFC-116 andHFC-23; PFC-116 and HFC-32; among others.

It is desirable to recycle any HF, which is recovered by practicing theinvention, for reuse as a reactant to manufacture PFC-116. However, itis generally undesirable to simultaneously recycle trace-organics withthe HF because such organics tend to become concentrated in the PFC-116product stream. While the best results are normally obtained byoperating the inventive process at process conditions that minimizeformation of HF-containing azeotropic or azeotrope-like compositions,such compositions may be used to purify recovered HF, as a PFC-116pre-purification step and/or to recover a useful product. TheHF-containing azeotropic or azeotrope-like compositions that can beformed consist essentially of one or more of the following mixtures: HFand PFC-116, HF and CFC-13, HF and HCFC-22, HF and CFC-113, HF andCFC-113a, HF and CFC-114, HF and CFC-114a, HF and CFC-115, HF andHFC-125, HF and HFC-143a, among others. Such HF-containing azeotropic orazeotrope-like compositions may be used to separate HF from the othercomponents, when, for example, PFC-116 is produced by the reaction of HFwith CFC-113, CFC-113a, CFC-114 and/or CFC-114a.

Whenever used in the specification and appended claims the terms beloware intended to have the following definitions.

By "azeotrope" or "azeotropic" composition is meant a constant boilingliquid admixture of two or more substances that behave as a singlesubstance. One way to characterize an azeotropic composition or mixtureis that the vapor produced by partial evaporation or distillation of theliquid has the same composition as the liquid from which it wasevaporated or distilled, e.g., the admixture distills/refluxes withoutcompositional change. Constant boiling compositions are characterized asazeotropic because they exhibit either a maximum or minimum boilingpoint, as compared with that of the non-azeotropic mixtures of the samecomponents. An azeotropic composition can also be characterized as themaximum or minimum vapor pressure for a mixture at a given temperaturewhen plotted as a function of liquid mole fraction.

By "azeotrope-like" composition is meant a constant boiling, orsubstantially constant boiling, liquid admixture of two or moresubstances that behaves as a single substance. One way to characterizean azeotrope-like composition is that the vapor produced by partialevaporation or distillation of the liquid has substantially the samecompositions as the liquid from which it was evaporated or distilled,e.g., the admixture distills/refluxes without substantial compositionalchange. An azeotrope-like composition can also be characterized by thearea, which is shown by plotting vapor pressure at given temperature asa function of liquid mole fraction, that is adjacent to the maximum orminimum vapor pressure.

Typically, a composition is azeotrope-like, if, after about 50 weight %of the composition is removed such as by evaporation or boiling off, thechange between the original composition and the composition remaining isless than about 6% and normally less than about 3% relative to theoriginal composition.

By "effective" amount is intended to refer to the amount of eachcomponent of the inventive compositions which, when combined, results inthe formation of an azeotropic or azeotrope-like composition. Thisdefinition includes the amounts of each component, which amounts mayvary depending on the pressure applied to the composition so long as theazeotropic or azeotrope-like compositions continue to exist at thedifferent pressures, but with possible different boiling points.Effective amount also includes the amounts, such as may be expressed inweight percentages, of each component of the compositions of the instantinvention which form azeotropic or azeotrope-like compositions attemperatures or pressures other than described herein. Therefore,included in this invention are azeotropic or azeotrope-like compositionsconsisting essentially of effective amounts of at least one of PFC-116and HCl, of PFC-116 and at least one fluorinated molecule, of HF and atleast one fluorinated molecule, of HCl and at least one fluorinatedmolecule such that after about 50 weight percent of an originalcomposition is evaporated or boiled off to produce a remainingcomposition, the change between the original composition and theremaining composition is typically no more than about 6% and normally nomore than about 3% or less relative to the original composition.

It is possible to characterize, in effect, a constant boiling admixturewhich may appear under many guises, depending upon the conditionschosen, by several criteria:

* The composition can be defined as an azeotrope of PFC-116 ("A") andHCl ("B"), or of PFC-116 ("C") and a Fluorinated Halocarbon ("D"), or ofHF ("E")and a Fluorinated Halocarbon ("F"), or of HCl ("G") and aFluorinated Halocarbon ("H") among others, because the term "azeotrope"is at once both definitive and limitative, and requires effectiveamounts of A,B(or C,D or E,F or G,H) for this unique composition ofmatter which can be a constant boiling composition.

* It is well known by those skilled in the art, that, at differentpressures, the composition of a given azeotrope will vary at least to adegree, and changes in pressure will also change, at least to somedegree, the boiling point temperature. Thus, an azeotrope of PFC-116("A") and HCl ("B"), or PFC-116 ("C") and a Fluorinated Halocarbon("D"), or of HF ("E") and a Fluorinated Halocarbon ("F"), or of HCl("G") and a Fluorinated Halocarbon ("H") among others, represents aunique type of relationship but with a variable composition whichdepends on temperature and/or pressure. Therefore, compositional ranges,rather than fixed compositions, are often used to define azeotropes.

* The composition can be defined as a particular weight percentrelationship or mole percent relationship of PFC-116("A") and HCl ("B"),or PFC-116 ("C") and a Fluorinated Halocarbon ("D"), or of HF ("E") anda Fluorinated Halocarbon ("F"), or of HCl ("G") and a FluorinatedHalocarbon ( "H") among others, while recognizing that such specificvalues point out only one particular relationship and that in actuality,a series of such relationships, presented by A,B (or C,D or E,F or G,H)actually exist for a given azeotrope, varied by the influence ofpressure.

* An azeotrope of PFC-116 ("A") and HCl ("B") or of PFC-116 ("C") and aFluorinated Halocarbon ("CD") or of HF ("E") and a FluorinatedHalocarbon ("F"), or of HCl ("G") and a Fluorinated Halocarbon ("H")among others, can be characterized by defining the compositions as anazeotrope characterized by a boiling point at a given pressure, thusgiven identifying characteristics without unduly limiting the scope ofthe invention by a specific numerical composition, which is limited byand is only as accurate as the analytical equipment available.

The azeotrope or azeotrope-like compositions of the present inventionmay be formed by operating a conventional distillation apparatus, whenpracticing the inventive distillation method, and by combining effectiveamounts of the components by any convenient method including mixing,combining, among others.

Recovered PFC-116, HCl, and HF can be purified simultaneously orindividually by using the aforementioned azeotropic and azeotrope-likecompositions in a process that comprises forming these azeotropic andazeotrope-like compositions within a conventional distillation column.For example, the conventional distillation column can be operated at atemperature and pressure that causes an azeotropic or azeotrope-likecomposition, which contains a desirable compound, to form therebypermitting removal of the composition, e.g., the impurities remain inthe column. Alternatively, the distillation column can operated underconditions that cause an azeotropic or azeotrope-like composition to beformed with an impurity wherein the impurity containing composition isremoved by distillation. Depending upon whether the azeotropic orazeotrope-like composition has a maximum or minimum boiling point, thecomposition will be collected, respectively, in the bottoms or as anoverhead product. For example, when the quantity of PFC-116 isrelatively large in comparison to undesired impurities, the PFC-116 canbe purified by introducing the PFC-116 to a distillation column whereinone or more azeotropic or azeotrope-like composition consistingessentially of, for example, HCl/PFC-116, PFC-116/CFC-13, PFC-116/HFC-23can be collected overhead as an overhead product in a distillationcolumn thereby leaving substantially pure PFC-116 as a bottoms product.

A key aspect of the invention relates to recovering substantially purePFC-116. In many cases, the PFC-116 possesses a purity that washeretofore impossible to achieve. The instant invention permitsobtaining PFC-116 that is at least 99.999 pure on a weight percent basiswhereas commercially available PFC-116 is typically only 99.99 wt %pure, e.g., the instant invention can produce 99.9999 wt % pure PFC-116.Such a purity is desirable for use in electronic industries as anetchant, e.g., in a plasma environment. Even very small amounts ofimpurity in a plasma etchant are believe to be undesirable, e.g., themarket value of the etchant is related to its purity. Consequently, theinstant invention provides a high purity PFC-116 product that solves theproblems associated with commercially available PFC-116.

The following Examples are provided to illustrate certain aspects of thepresent invention; but not limit the scope of the appended claims. Partsper million (ppm) are by weight based upon only the fluorocarbonspresent, and do not include the weights of any acids present in thecalculation unless otherwise indicated. The following Examples employthe NRTL interaction parameters identified above. In the followingExamples, each stage is based upon a 100% operational or performanceefficiency. The following Examples compare the application ofconventional distillation methods with the processes of this inventionfor various mixtures of PFC-116 with other fluorocarbon impurities. Inall examples, the numbering of separation stages is based on theconvention that the condenser is counted as stage number 1. For purposesof comparison, a 98% recovery of essentially pure PFC-116 containing 1ppm or less of impurity has been chosen as a goal.

EXAMPLES Comparative Example 1

In this Example, conventional distillation is used in a column with 62stages for purifying a feed stream containing 500 lb/hr ofhexafluoroethane (PFC-116) and 0.5 lb/hr of chlorotrifluoromethane(CFC-13) (a nominal concentration of 1000 ppm). The feed stream isintroduced onto stage 25. The feed is introduced at a temperature of -25degrees C., with the column condenser pressure set at 124.7 psia and thecolumn base pressure 3 psi higher. The column distillate/feed ratio isvaried to get the specified product recovery, and the reflux ratio isvaried to approximately meet the hexafluoroethane specification of 1 ppmof chlorotrifluoromethane in the column bottoms. In this Example thedistillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 beingfed to the column. The bottoms temperature is -26 degrees C. and thedistillate temperature is -27 degrees C. The hexafluoroethane productleaves from the bottom of the column; the chlorotrifluoromethane andsome of the hexafluoroethane leave in the column distillate. The resultsare shown in Table 9 below.

                  TABLE 9                                                         ______________________________________                                        Dist./Feed                                                                            Reflux  ppm CFC-13 Lb/hr PFC-116                                                                          % PFC-116                                 Ratio   Ratio   in Bottoms in Bottoms                                                                             Recovery                                  ______________________________________                                        0.10    170     1.0        451      90                                        0.05    400     1.0        476      95                                        0.02    1520    1.0        491      98                                        ______________________________________                                    

Conventional distillation can recover about 98% of the PFC-116 in thefeed while producing a product with about 1 ppm of CFC-13 by using areflux ratio of over 1000 to 1. Such a reflux ratio would requirerelatively large equipment and an uneconomically high heating andcooling energy load. The recovery efficiency of the PFC-116 is limitedbecause an azeotropic or azeotrope-like composition is formed betweenPFC-116 and CFC-13 that exits the column as the distillate in thisExample. However, this Example illustrates how the concentration ofCFC-13 can be reduced from a first or feed mixture comprising PFC-116and CFC-13 by using azeotropic distillation.

Comparative Example 2

In this Example, conventional distillation is used in a column with 62stages for purifying a feed stream containing 500 lb/hr ofhexafluoroethane (PFC-116), 0.5 lb/hr of chlorotrifluoroethane (CFC-13)and 0.5 lb/hr of trifluoromethane (HFC-23) (a nominal concentration of1000 ppm each). The feed stream is introduced onto stage 25. The feed isintroduced at a temperature of -25 degrees C., with the column condenserpressure set at 154.7 psia and the column base pressure 3 psi higher.The column distillate/feed ratio is varied to get the specified productrecovery, and the reflux ratio is varied to meet the hexafluoroethanespecification of 1 ppm of CFC-13 plus HFC-23 in the column bottoms. Inthis Example the distillate/feed ratio refers to the ratio of the totalmoles of all species being removed in the distillate to the moles ofPFC-116 in the feed to the column. The bottoms temperature is -19degrees C. and the distillate temperature varies from -21 to -25 degreesC. depending on the distillate/feed ratio and reflux ratio. Thehexafluoroethane product leaves from the bottom of the column; theHFC-23, CFC-13 and a portion of the hexafluoroethane leave in the columndistillate. The results are shown in Table 10 below.

                  TABLE 10                                                        ______________________________________                                        Dist./        ppm       ppm     Lb/hr   %                                     Feed  Reflux  CFC-13    HFC-23  PFC-116 PFC-116                               Ratio Ratio   in Bottoms                                                                              in Bottoms                                                                            in Bottoms                                                                            Recovery                              ______________________________________                                        0.10  161     1.0       <0.01   452     90                                    0.05  377     1.0       <0.01   477     95                                    0.02  1526    1.0       <0.01   492     98                                    ______________________________________                                    

Table 10 shows that the ability to obtain substantially pure PFC-116with this process is the same as in Comparative Example 1 in that thepresence of CFC-13 limits the efficiency of the process. Even though theHFC-23 can be removed to relatively low levels by using conventionaldistillation, when in combination with CFC-13, an uneconomical refluxratio of about 1500 to 1 is required to achieve an overall impuritylevel of less than about 1 ppm and 98% recovery of PFC-116. The recoveryefficiency of the PFC-116 is limited because azeotropic orazeotrope-like compositions are formed between PFC-116 and CFC-13, andPFC-116 and HFC-23. However, this Example illustrates how theconcentration of HFC-23 can be reduced from a feedstock or first mixturecomprising PFC-116 and at least HFC-23 by using azeotropic distillation.

Example 1

In this Example, azeotropic distillation with HCl is used in a columnwith 62 stages for purifying a feed stream coming 500 lb/hr ofhexafluoroethane (PFC-116) and 0.5 lb/hr of chlorotrifluoromethane(CFC-13), the same composition as Comparative Example 1. To this isadded 250 lb/hr of anhydrous HCl. The feed stream is introduced ontostage 41. The feed is introduced at a temperature of -30 degrees C.,with the column condenser pressure set at 264.7 psia and the column basepressure 3 psi higher. The column distillate/feed ratio is varied to getthe specified product recovery, and the reflux ratio is varied toapproximately meet the hexafluoroethane specification of 1 ppm ofchlorotrifluoromethane in the column distillate. In this Example thedistillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 and HClin the feed to the column. The distillate temperature is -27 degrees C.and the bottom column temperature varies from -26 to -21 degrees C.depending the distillate/feed ratio. In this Example, thehexafluoroethane product leaves in the column distillate stream as anazeotropic or azeotrope-like composition with HCl; the remaining HCl andchlorotrifluoromethane exit in the column bottoms. The results are shownin Table 11 below.

                  TABLE 11                                                        ______________________________________                                        Dist./Feed                                                                            Reflux  ppm CFC-13 Lb/hr PFC-116                                                                          % PFC-116                                 Ratio   Ratio   Overhead   in Overhead                                                                            Recovery                                  ______________________________________                                        0.83    12.5    1.1        450      90                                        0.88    13.2    1.1        475      95                                        0.91    14.6    1.0        490      98                                        0.92    16.4    1.0        495      99                                        ______________________________________                                    

The above Example shows that PFC-116 may be recovered with an impuritylevel of less than about 1 ppm of CFC-13 and a yield of 99% by using HClas an azeotroping agent.

The PFC-116 and azeotroped HCl are then cooled to a temperature belowabout -50 degrees C. and the two layers separated in a decanter. ThePFC-116 layer is then sent to a second distillation column for removingthe remaining HCl as an overhead azeotrope; the recovered HCl may thenbe recycled to the first distillation column. The PFC-116 from thebottoms of the second distillation column is then given any finalpurification steps required by using procedures well known to thoseskilled in the art, e.g., passing the PFC-116 through a resin bed fordeacidification.

Example 2

Example 1 is substantially repeated but with the addition of 0.3 lb/hreach of HCFC-22 and HFC-125 to the previous feed mixture of PFC-116 andCFC-13. The results are substantially identical to the previous Example1 except that the removal of HCFC-22 and of HFC-125 to the bottom streamis even more efficient than that of CFC-13. The overhead product PFC-116in this case contains only 0.001 ppm each of HCFC-22 and HFC-125 alongwith the previously reported amount of CFC-13.

Example 3

In this Example, azeotropic distillation with HCl is used in a firstcolumn with 62 stages for purifying a feed stream containing 500 lb/hrof hexafluoroethane (PFC-116), 0.5 lb/hr of chlorotrifluoromethane(CFC-13), and 0.5 lb/hr of trifluoromethane (HFC-23), which correspondsto the composition of Comparative Example 2, plus an added 250 lb/hr ofanhydrous HCl. The feed stream is introduced onto stage 41 of the firstdistillation column at a temperature of -37 degrees C. A recycle streamfrom a second distillation column containing 604 lb/hr PFC-116, <0.01lb/hr CFC-13, 9.9 lb/hr HFC-23, 487 lb/hr HCl is introduced to the firstdistillation column without heating or cooling at stage 21. The firstcolumn condenser pressure is set at 264.7 psia and the first column basepressure 3 psi higher. The first column is operated at a 10/1 refluxratio. The column distillate rate is varied so that 99.5% of the totalPFC-116 fed to the column is recovered in the column distillate. Thedistillate temperature is -27 degrees C. and the bottom columntemperature is -14 degrees C. The results of this distillation are shownin Table 12.

                  TABLE 12                                                        ______________________________________                                        (First Column)                                                                Reflux                                                                              ppm CFC-13                                                                              ppm HFC-23 Lb/hr PFC-116                                                                          % PFC-116                                 Ratio in Overhead                                                                             in Overhead                                                                              in Overhead                                                                            Recovery                                  ______________________________________                                        10    0.14      8927       1099     99.5                                      ______________________________________                                    

The 99.5% PFC-116 recovery is calculated as the percent of total PFC-116in the column (feed stock plus recycle) which is recovered in thedistillate. In the first column the majority of the hexafluoroethaneexits in the column distillate stream as an azeotropic or azeotrope-likecomposition with HCl along with a portion of the HFC-23; the remainingHCl, HFC-23 and the CFC-13 leave in the first column bottoms. On anHFC-23 basis, 0.5 lb/hr of HFC-23 enters the first column as the feedstock and an additional 9.9 lb/hr with the recycle stream. Leaving thecolumn, 0.5 lb/hr of HFC-23 is in the bottoms stream and 9.9 lb/hr ofHFC-23 is in the distillate. By increasing the total HFC-23 content inthe first column, the relative volatility of HFC-23 is such that all theHFC-23 entering the first column as a feedstock is forced to the bottomof the first column and removed in the bottom stream. The remainder ofthe HFC-23 exits the first column via the distillate, but is recycledback to this first column by way of the decanter and second column theoverall system as detailed below.

The HCl-hexafluoroethane azeotropic or azeotrope-like composition isthen cooled to -55 degrees C. and fed to a decanter for phaseseparation. The results of the decantation step are given below in theTable 13:

                  TABLE 13                                                        ______________________________________                                        (Decanter)                                                                            Stream from                                                                   First Column                                                                             HCl-Rich Phase                                                     Distillate-                                                                              From Decanter                                                                             PFC-116 Rich Phase                             Component                                                                             Feed Stream                                                                              Top Stream  From Decanter                                  (Lb/hr) (Lb/hr)    (Lb/hr)     Bottom Stream                                  ______________________________________                                        HCl     487        310         177                                            CFC-13  <0.01      <0.01       <0.01                                          HFC-23  9.9        1.0         8.9                                            PFC-116 1099       110         989                                            ______________________________________                                    

The HCl-rich phase, which forms in the upper region of the decanter, isreturned in a recycle stream to the first column.

The hexafluoroethane-rich phase, which forms in the bottom region of thedecanter, is then fed to a second distillation column with 52theoretical stages with the feed at stage 10. The second columncondenser pressure is set at 324.7 psia. The second column is operatedat a reflux ratio of 3/1. The distillate temperature is -20 degrees C.and the bottom column temperature is 7.5 degrees C. In this secondcolumn, the purified hexafluoroethane leaves the bottom of the column,and the recycle stream to the first column leaves in the overhead. Theresults of this distillation are shown in Table 14. In this Example, thebottoms/feed ratio is the ratio of the moles of PFC-116 exiting thecolumn in the column bottoms to the moles of PFC-116 being fed to thecolumn.

                  TABLE 14                                                        ______________________________________                                        (Second Column)                                                                             ppm      ppm   ppm    Lb/hr                                     Bott./        CFC-13   HFC-23                                                                              HCl    PFC-  %                                   Feed  Reflux  in       in    in     116 in                                                                              PFC-116                             Ratio Ratio   Bottoms  Bottoms                                                                             Bottoms                                                                              Bottoms                                                                             Recovery                            ______________________________________                                        0.5   3       <0.01    <0.01 <0.01  494   50                                  ______________________________________                                    

The bottoms stream from this second column is the product PFC-116, whichmay then be sent on to further purification if desired. The PFC-116recovery in the second column is 50% because the remaining approximately50% of the PFC-116 is recycled to the first column. The overall recoveryfor the system (first column, decanter, second column) is however 99.0%.This Example shows that substantially pure PFC-116 can be obtained at ahigh rate of recovery by using azeotropic distillation. The productPFC-116 obtained from the bottoms of the second column from this overallsystem is substantially free of both halocarbons and HCl. This Exampleshow that the invention can produce a PFC-116 product that is greaterthan 99.999 wt % PFC-116 based on the weight of all components containedwithin.

Example 4

In this Example, the amounts of CFC-13 and HFC-23 are increased tentimes in comparison to Example 3. Other conditions are essentially thesame. The results of this Example are listed below in Tables 15, 16 and17.

                  TABLE 15                                                        ______________________________________                                        (First Column)                                                                Reflux                                                                              ppm CFC-13                                                                              ppm HFC-23 Lb/hr PFC-116                                                                          % PFC-116                                 Ratio in Overhead                                                                             in Overhead                                                                              in Overhead                                                                            Recovery                                  ______________________________________                                        10    0.69      30009      1099     99.5                                      ______________________________________                                    

                  TABLE 16                                                        ______________________________________                                        (Decanter)                                                                              Feed Stream Top Stream                                                                              Bottom Stream                                 Component Lb/hr       Lb/hr     Lb/hr                                         ______________________________________                                        HCl       486         301       185                                           CFC-13    <0.01       <0.01     <0.01                                         HFC-23    34.1        3.4       30.7                                          PFC-116   1098.8      109.9     988.9                                         ______________________________________                                    

The top stream is recycled back to the first distillation column, andthe bottoms stream fed to the second distillation column as in Example3.

                  TABLE 17                                                        ______________________________________                                        (Second Column)                                                                             ppm      ppm   ppm    Lb/hr                                     Bott./        CFC-13   HFC-23                                                                              HCl    PFC-  %                                   Feed  Reflux  in       in    in     116 in                                                                              PFC-116                             Ratio Ratio   Bottoms  Bottoms                                                                             Bottoms                                                                              Bottoms                                                                             Recovery                            ______________________________________                                        0.5   3       <0.01    <0.01 <0.01  494   50                                  ______________________________________                                    

The distillate stream from the second column is recycled back to thefirst column as in Example 3.

This Example demonstrates that PFC-116/HCl azeotropic distillation canbe used for purifying a PFC-116 feedstock or product that has ten timesthe amount of CFC-13 and HFC-23 as Example 3 and Comparative Example 2.The product PFC-116 obtained from the bottoms of the second column fromthis overall system is substantially free of both halocarbons and HCl.The overall recovery of PFC-116 is 99%. This Example shows that theinvention can produce a PFC-116 product that is greater than 99.999 wt %PFC-116 based on the weight of all components contained within.

Example 5

In this Example, azeotropic distillation is used to purify HCl in acolumn with 52 stages. The feed stream contains 250 lb/hr of anhydrousHCl, 100 lb/hr of hexafluoroethane (PFC-116), 0.5 lb/hr ofchlorotrifluoromethane (CFC-13), and 0.5 lb/hr of trifluoromethane(HFC-23). The feed stream is introduced onto stage 10. The feed isintroduced at a temperature of -25 degrees C., with the column condenserpressure set at 314.7 psia and the column base pressure 3 psi higher.The reflux ratio is held constant at 3/1 while the column bottoms/feedratio is varied. The temperature of the bottoms stream is -21 degreesC.; the temperature of the overhead is -6 to -9 degrees C. depending onthe bottom/feed ratio. In this column, substantially pure HCl exits thecolumn bottoms stream and the HCl/PFC-116 azeotrope leaves in theoverhead stream along with the other impurities (CFC-13 and HFC-23). Ina fully integrated system, the feed to this column would be similar incomposition to that of the acid-rich phase from the previously describeddecanter, and the overhead from this distillation column would berecycled back to the decanter or the first distillation column toimprove the overall recovery rate of all ingredients. The results areshown in Table 18 below.

                  TABLE 18                                                        ______________________________________                                               ppm      ppm      ppm    Lb/hr                                         Bott./ CFC-13   HFC-23   PFC-116                                                                              HCl    %                                      Feed   in       in       in     in     HCl                                    Ratio  Bottoms  Bottoms  Bottoms                                                                              Bottoms                                                                              Recovery                               ______________________________________                                        0.65   <0.01    <0.01    <0.01  163    65                                     0.70   <0.01    <0.01    <0.01  175    70                                     0.75   <0.01    <0.01    <0.01  188    75                                     0.80   <0.01     0.02    <0.01  200    80                                     0.85   1894     1618     45354  210    84                                     ______________________________________                                    

Table 18 illustrates that the impurities in the product HCl can besubstantially removed by performing a distillation operation underappropriate conditions. The level of impurities remains relatively lowas the bottom/feed ratio is increased from 0.65 to 0.80, but at abottom/feed ratio of about 0.85 there is insufficient HCl in the columnto carry off the impurities in the overhead stream, and the impuritylevel in the HCl sharply increases to an undesirable level. The impurityconcentration increases when the amount of HCl in the distillationcolumn is less than that necessary to form the PFC-116/HCl azeotropic orazeotrope-like compositions, e.g., less than about 62 mole percent ofHCl. The overall HCl recovery rate that can be achieved by using theprocesses of this invention in an integrated system, i.e., with recycleof the overhead stream, would be near 100%.

Comparative Example 3

In this Example, azeotropic distillation is used to obtain purified HFfrom a mixture containing PFC-116 within a distillation column having 62stages. The feed stream contains 1900 lb/hr of anhydrous HF and 690lb/hr of hexafluoroethane (PFC-116). The feed stream is introduced ontostage 25. The feed is introduced at a temperature of -25 degrees C.,with the column condenser pressure set at 164.7 psia and the column basepressure 3 psi higher. The reflux ratio is held constant at 2/1 whilethe column distillate/feed ratio is varied. The temperature of thebottoms stream is 104 degrees C.; the temperature of the overhead is -17to -18 degrees C. depending on the distillate/feed ratio. In thisExample the distillate/feed ratio refers to the ratio of the total molesof all species being removed in the distillate to the moles of PFC-116in the feed to the column. In this column, the substantially pure HFexits in the column bottoms stream and the HF/PFC-116 azeotropic orazeotrope-like composition exits in the overhead stream. The results areshown in Table 19 below.

                  TABLE 19                                                        ______________________________________                                              ppm      Lb/hr     Lb/hr  Lb/hr                                         Dist./                                                                              PFC-116  HF        PFC-116                                                                              HF      %                                     Feed  in       in        in     in      HF                                    Ratio Bottoms  Bottoms   Overhead                                                                             Overhead                                                                              Recovery                              ______________________________________                                        2.0   0.0      1800      690    100     94.7                                  1.5   0.0      1850      690    50      97.4                                  1.25  0.0      1875      690    25      98.7                                  1.1   0.0      1890      690    10      99.5                                  ______________________________________                                    

This Example shows that the HF/PFC-116 azeotropic or azeotrope-likecompositions have a relatively high volatility in comparison to HFthereby enabling substantially all of the PFC-116 to be removed from theHF as an azeotrope composition. This process forms an overhead streamthat consists essentially of PFC-116/HF mixture. In order to recover thePFC-116 as a pure product, the PFC-116 could be scrubbed with water

Comparative Example 4

In this Example, azeotropic distillation is used to purify PFC-116 froma mixture with HF in a column with 62 stages. The feed stream contains100 lb/hr of anhydrous HF (5 moles) and 13,112 lb/hr of hexafluoroethane(PFC-116) (95 moles). The feed stream is introduced onto stage 25. Thefeed is introduced at a temperature of -25 degrees C., with the columncondenser pressure set at 164.7 psia and the column base pressure 3 psihigher. The reflux ratio is held constant at 10/1 while the columndistillate/feed ratio is varied. The temperature of the overhead streamis -17.7 degrees C.; the temperature of the bottoms is -16.4 to -16.9degrees C. depending on the distillate/feed ratio. In this column, thegoal is to take the HF/PFC-116 azeotrope overhead and recover a purifiedPFC-116 in the bottoms stream. In this Example, the distillate-to-feedratio refers to the ratio of total moles of all species being removed inthe distillate to the moles of HF in the feed to the column. The resultsare shown in Table 20 below.

                  TABLE 20                                                        ______________________________________                                              ppm      Lb/hr     Lb/hr                                                Dist./                                                                              HF       PFC-116   PFC-116                                                                              Lb/hr   %                                     Feed  in       in        in     HF      PFC-116                               Ratio Bottoms  Bottoms   Overhead                                                                             Overhead                                                                              Recovery                              ______________________________________                                        5     3683     10,094    3018   63      77.0                                  4     4640     10,698    2414   50      81.6                                  3     5493     11,301    1811   38      86.2                                  2     6258     11,905    1207   25      90.8                                  1     6948     12,508     604   13      95.4                                  ______________________________________                                    

This Example shows a low degree of purification when operating thedistillation column under these conditions because the volatility of theHF/PFC-116 azeotrope is similar to PFC-116.

Example 6

In this Example, azeotropic distillation is used to separate PFC-116from a mixture with HF by adding HCl to the mixture. A column with 62stages is used with the feed introduced onto stage 25. The feed streamcontains 1000 lb/hr of anhydrous HF (50 moles), 6,901 lb/hr ofhexafluoro-ethane (PFC-116) (50 moles), and 3,646 lb/hr of HCl (100moles). The feed is introduced at a temperature of -25 degrees C., withthe column condenser pressure set at 164.7 psia and the column basepressure 3 psi higher. The reflux ratio is held constant at 3/1 whilethe column distillate/feed ratio is adjusted to recover 99.9% of thePFC-116 overhead. In this Example the distillate/feed ratio refers tothe ratio of the total moles of all species being removed in thedistillate to the moles of PFC-116 and HCl in the feed to the column.The temperature of the overhead stream is -41.6 degrees C.; thetemperature of the bottoms is -20.2 degrees C. In this column, the goalis to take the HCl/PFC-116 azeotropic or azeotrope-like compositionoverhead and leave the pure HF and remaining HCl in the bottoms stream.The results are shown in Table 21 below.

                  TABLE 21                                                        ______________________________________                                        ppm      Lb/hr    Lb/hr      Lb/hr   %                                        HF in    HCl in   PFC-116 in PFC-116 in                                                                            PFC-116                                  Overhead Overhead Overhead   Bottoms Recovery                                 ______________________________________                                        0.0      2960     6894       6.9     99.9                                     ______________________________________                                    

In contrast to comparative Examples 3 and 4, where HF and PFC-116 werevirtually inseparable, this Example shows how the separation of HF andPFC-116 may be effected by forming an HCl/PFC-116 azeotropic orazeotrope-like composition. Best results are obtained when the quantityof HCl is sufficient to form the azeotropic or azeotrope-likecomposition. The HCl/HF mixture in the bottoms stream can be separatedby distillation. If the amount of HCl is minimized, the HF can berecycled to a PFC-116 manufacturing process, i.e., a relatively smallamount of HCl will not interfere with the PFC-116 reaction. TheHCl/PFC-116 azeotropic or azeotrope-like composition is readilyseparable into its individual components by the previously describeddecantation and distillation processes.

Comparative Example 5

In this Example, conventional distillation is used in a column with 62stages for purifying a feed stream containing 500 lb/hr ofhexafluoroethane (PFC-116) and 0.5 lb/hr of difluoromethane (HFC-32) (anominal concentration of 1000 ppm). The feed stream is introduced ontostage 25. The feed is introduced at a temperature of -5 degrees C., withthe column condenser pressure set at 264.7 psia and the column basepressure 3 psi higher. The column distillate/feed ratio is varied to getthe specified product recovery, and the reflux ratio is varied toapproximately meet the hexafluoroethane specification of 1 ppm ofdifluoromethane in the column bottoms. In this Example thedistillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 in thefeed to the column. The bottoms temperature and the distillatetemperature vary as shown. The hexafluoroethane product leaves from thebottom of the column; the difluoromethane and some of thehexafluoroethane leave in the column distillate. The results are shownin Table 22 below.

                  TABLE 22                                                        ______________________________________                                                               % PFC-116                                                                                       Re-                                  Dist./       Distillate    Bottoms       covery                               Feed Reflux  116    32   Temp  116  32   Temp  in                             Ratio                                                                              Ratio   Lb/hr  Lb/hr                                                                              Deg C.                                                                              Lb/hr                                                                              PPM  Deg C.                                                                              Bottoms                        ______________________________________                                        0.10 13.2    48.7   0.50 -1.8  451  1.0  0     90.3                           0.05 28.8    23.7   0.50 -2.9  476  1.0  0     95.3                           0.02 75.6    8.7    0.50 -5.2  491  1.0  0     98.3                           0.01 151     3.7    0.50 -6.3  496  1.0  0     99.3                           ______________________________________                                    

Conventional distillation can recover about 99% of the PFC-116 in thefeed while producing a product with about 1 ppm of HFC-32 by using areflux ratio of over 150 to 1. However, such a reflux ratio wouldrequire relatively large equipment and an uneconomically high heatingand cooling energy load. The recovery efficiency of the PFC-116 islimited because an azeotropic or azeotrope-like composition is formedbetween PFC-116 and HFC-32 that exits the column as the distillate inthis Example. However, this Example illustrates how the concentration ofHFC-32 can be reduced from a first or feed mixture comprising PFC-116and HFC-32 by using azeotropic distillation.

Example 7

In this Example, azeotropic distillation is used to separate PFC-116from a mixture with HFC-32 by adding HCl to the mixture. A column with42 stages is used with the feed introduced onto stage 28. The feedstream contains 500 lb/hr of hexafluoroethane (PFC-116), 0.5 lb/hr ofHFC-32, and 250 lb/hr of HCl. The feed is introduced at a temperature of-30 degrees C., with the column condenser pressure set at 264.7 psia andthe column base pressure 3 psi higher. The column distillate/feed ratiois held constant while the reflux ratio is varied. In this Example thedistillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 and HClin the feed to the column. The temperature of the overhead stream is-26.8 degrees C.; the temperature of the bottoms is -12.0 degrees C. Inthis column, the goal is to take the HCl/PFC-116 azeotropic orazeotrope-like composition overhead and leave the HFC-32 in the bottomsstream. The results are shown in Table 23 below.

                  TABLE 23                                                        ______________________________________                                        Dist./       Distillate   Bottoms    % PFC-116                                Feed Reflux  116    HCl  32   116  HCl  32   Recovery                         Ratio                                                                              Ratio   Lb/hr  Lb/hr                                                                              ppm  Lb/hr                                                                              pph  Lb/hr                                                                              in Distillate                    ______________________________________                                        0.95 10      500    231  <.01 <.01 19   0.5  100                              0.95 3       500    231  <.01 <.01 19   0.5  100                              0.95 1       500    231  <.01 <.01 19   0.5  100                              ______________________________________                                    

In contrast to Comparative Example 5, when HCl is added to the 32/116mixture, essentially complete separation of the HFC-32 and PFC-116 maybe effected. The PFC-116/HCl product exiting as the distillate may beseparated by decanting and subsequent azeotropic distillation. TheHFC-32/HCl mixture exiting the bottoms may be separated by conventionaldistillation.

Comparative Example 6

In this Example, conventional distillation is used in a column with 62stages for purifying a feed stream containing 500 lb/hr ofhexafluoroethane (PFC-116) and 0.5 lb/hr of 1,1,1-trifluoroethane(HFC-143a) (a nominal concentration of 1000 ppm). The feed stream isintroduced onto stage 25. The feed is introduced at a temperature of -15degrees C., with the column condenser pressure set at 64.7 psia and thecolumn base pressure 3 psi higher. The reflux ratio is fixed and thecolumn distillate/feed ratio is varied to get the specified productrecovery, with the goal to obtain a maximum of 100 ppm oftrifluoroethane in the PFC-116 product. In this Example thedistillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 in thefeed to the column. The bottoms temperature and the distillatetemperature are as shown. The hexafluoroethane product leaves from thetop of the column; the trifluoroethane and some of the hexafluoroethaneleave in the column bottoms. The results are shown in Table 24 below.

                  TABLE 24                                                        ______________________________________                                                               % PFC-116                                                                                       Re-                                  Dist./       Distillate    Bottoms       covery                               Feed Reflux  116    143a Temp  116  143a Temp  Dis-                           Ratio                                                                              Ratio   Lb/hr  ppm  Deg C.                                                                              Lb/hr                                                                              Lb/hr                                                                              Deg C.                                                                              tillate                        ______________________________________                                        0.98 100     490    551  -45.5 10   0.23 -44.2 98.0                           0.90 100     450    346  -45.5 50   0.34 -44.3 90.0                           0.50 100     250    187  -45.5 250  0.45 -44.3 50.0                           0.10 100      50    264  -45.5 450  0.49 -44.3 10.0                           0.02 100      10    336  -45.5 490  0.50 -44.3 2.0                            ______________________________________                                    

At these column pressures and temperatures, conventional distillationcannot produce the desired 100 ppm HFC-143a in the product PFC-116 at areflux ratio of 100:1 because of the vapor-liquid equilibrium tangentpinch which exists between PFC-116 and HFC-143a. Moreover, columnoperation to obtain the separation requires extremely cold temperaturesand high reflux ratios, the combination of which are extremely expensiveto provide.

EXAMPLE 8

In this Example, azeotropic distillation is used to separate PFC-116from a mixture with HFC-143a by adding HCl to the mixture. A column with42 stages is used with the feed introduced onto stage 28. The feedstream contains 500 lb/hr of hexafluoroethane (PFC-116), 0.5 lb/hr ofHFC-143a, and 250 lb/hr of HCl. The feed is introduced at a temperatureof -30 degrees C., with the column condenser pressure set at 264.7 psiaand the column base pressure 3 psi higher. The column distillate/feedratio is held constant while the reflux ratio is varied. In this Examplethe distillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 and HClin the feed to the column. The temperature of the overhead stream is-26.8 degrees C.; the temperature of the bottoms is -12.2 degrees C. Inthis column, the goal is to take the HCl/PFC-116 azeotropic orazeotrope-like composition overhead and leave the HFC-143a in thebottoms stream. The results are shown in Table 25 below.

                  TABLE 25                                                        ______________________________________                                                               % PFC-116                                                                                       Re-                                  Dist./       Distillate    Bottoms       covery                               Feed Reflux  116    HCl  143a  116  HCl  143a  in Dis-                        Ratio                                                                              Ratio   Lb/hr  Lb/hr                                                                              ppm   Lb/hr                                                                              pph  Lb/hr tillate                        ______________________________________                                        0.95 10      500    231  <.01  <.01 19   0.5   100                            0.95 3       500    231  <.01  <.01 19   0.5   100                            0.95 1       500    231  3.8   <.01 19   0.5   100                            ______________________________________                                    

In contrast to Comparative Example 6, when HCl is added to the 143a/116mixture, essentially complete separation of the HFC-143a and PFC-116 maybe effected, and in contrast to Comparative Example 6, this isaccomplished with both higher temperature and lower reflux ratiooperation. The PFC-116/HCl product exiting as the distillate may beseparated by decanting and subsequent azeotropic distillation. TheHFC-143a/HCl mixture exiting the bottoms may be separated byconventional distillation.

Comparative Example 7

In this Example, conventional distillation is used in a column with 62stages for purifying a feed stream containing 500 lb/hr ofhexafluoroethane (PFC-116) and 0.5 lb/hr of 1,1-difluoroethane(HFC-152a) (a nominal concentration of 1000 ppm). The feed stream isintroduced onto stage 25. The feed is introduced at a temperature of -15degrees C., with the column condenser pressure set at 64.7 psia and thecolumn base pressure 3 psi higher. The reflux ratio is fixed and thecolumn distillate/feed ratio is varied to get the specified productrecovery, with the goal to obtain a maximum of 100 ppm of HFC-152a inthe PFC-116 product. In this Example the distillate/feed ratio refers tothe ratio of the total moles of all species being removed in thedistillate to the moles of PFC-116 in the feed to the column. Thebottoms temperature and the distillate temperature are as shown. Thehexafluoroethane product leaves from the top of the column; thetrifluoroethane and some of the hexafluoroethane leave in the columnbottoms. The results are shown in Table 26 below.

                  TABLE 26                                                        ______________________________________                                                               % PFC-116                                                                                       Re-                                  Dist./       Distillate    Bottoms       covery                               Feed Reflux  116    152a Temp  116  152a Temp  Dis-                           Ratio                                                                              Ratio   Lb/hr  ppm  Deg C.                                                                              Lb/hr                                                                              Lb/hr                                                                              Deg C.                                                                              tillate                        ______________________________________                                        0.98 100     489    1013 -45.5  11  0.01 -44.3 97.8                           0.90 100     449    1065 -45.5  51  0.02 -44.3 89.8                           0.50 100     249    1318 -45.5 251  0.17 -44.3 49.9                           0.10 100      50    1339 -45.5 475  0.43 -44.3 10.0                           0.02 100      10    1271 -45.5 490  0.49 -44.3 2.0                            ______________________________________                                    

At these column pressures and temperatures, conventional distillationcannot produce the desired 100 ppm HFC-152a in the product PFC-116 at areflux ratio of 100:1 because of the vapor-liquid equilibrium tangentpinch which exists between PFC-116 and HFC-152a. Moreover, columnoperation to obtain the separation requires extremely cold temperaturesand high reflux ratios, the combination of which are extremely expensiveto provide.

EXAMPLE 9

In this Example, azeotropic distillation is used to separate PFC-116from a mixture with HFC-152a by adding HCl to the mixture. A column with42 stages is used with the feed introduced onto stage 28. The feedstream contains 500 lb/hr of hexafluoroethane (PFC-116), 0.5 lb/hr ofHFC-152a, and 250 lb/hr of HCl. The feed is introduced at a temperatureof -30 degrees C., with the column condenser pressure set at 264.7 psiaand the column base pressure 3 psi higher. The column distillate/feedratio is held constant while the reflux ratio is varied. In this Examplethe distillate/feed ratio refers to the ratio of the total moles of allspecies being removed in the distillate to the moles of PFC-116 and HClin the feed to the column. The temperature of the overhead stream is-26.8 degrees C.; the temperature of the bottom is -11.9 degrees C. Inthis column, the goal is to take the HCl/PFC-116 azeotropic orazeotrope-like composition overhead and leave the HFC-152a in thebottoms stream. The results are shown in Table 27 below.

                  TABLE 27                                                        ______________________________________                                                               % PFC-116                                                                                       Re-                                  Dist./       Distillate    Bottoms       covery                               Feed Reflux  116    HCl  152a  116  HCl  152a  Dis-                           Ratio                                                                              Ratio   Lb/hr  Lb/hr                                                                              ppm   Lb/hr                                                                              pph  Lb/hr tillate                        ______________________________________                                        0.95 10      500    231  <.01  <.01 19   0.5   100                            0.95 3       500    231  <.01  <.01 19   0.5   100                            0.95 1       500    231  <.01  <.01 19   0.5   100                            ______________________________________                                    

In contrast to Comparative Example 7, when HCl is added to the 152a/116mixture, essentially complete separation of the HFC-152a and PFC-116 maybe effected without expensive low temperature and high reflux operation.The PFC-116/HCl product exiting as the distillate may be separated bydecanting and subsequent azeotropic distillation. The HFC-152a/HClmixture exiting the bottoms may be separated by conventionaldistillation.

EXAMPLE 10

This Example demonstrates the existence of azeotropic or azeotrope-likecompositions between the binary pair mixtures consisting essentially ofHCl and PFC-116; HCl and CFC-13; HCl and HFC-23; HCl and CFC-115; HF andPFC-116; PFC-116 and CFC-13; PFC-116 and HFC-23; PFC-116 and HFC-32; HFand CFC-115; HF and CFC-114; HF and CFC-114a; HF and CFC-113; HFandCFC-113a; HF and HFC-125; CFC-13 and HF; HF and HCFC-22; HF andHFC-143a. To determine the relative volatility of each binary pair, theso-called PTx Method was used. In this procedure, for each binary pair,the total absolute pressure in a PTx cell of known volume was measuredat a constant temperature for various known binary compositions. Thesemeasurements were then reduced to equilibrium vapor and liquidcompositions using the NRTL equation. Samples of selected vapor andliquid sets were obtained and analyzed to verify their respectivecompositions.

The vapor pressure measured versus the composition in the PTx cell forthe HCl and PFC-116; HCl and CFC-13; HCl and HFC-23; HCl and CFC-115; HFand PFC-116; PFC-116 and CFC-13; PFC-116 and HFC-23; PFC-116 and HFC-32;HF and CFC-115; HF and CFC-114; HF and CFC-114a; HF and CFC-113; HF andCFC-113a; HF and HFC-125; CFC-13 and HF; HF and HCFC-22; HF and HFC-143asystems are shown in FIGS. 2 through 20, respectively. The experimentaldata points are shown in each Figure as solid points on each Figure andthe curve is drawn from data calculated using the NRTL equation.

Referring now to FIG. 2, FIG. 2 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHCl and PFC-116 at -20.56 deg C., as indicated by a mixture of about63.0 mole % HCl and 37.0 mole % PFC-116 having the highest pressure overthe range of compositions at this temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 60.5 mole % HCl and 39.5 mole % PFC-116 is formedat -60 deg C. and 80.6 psia and an azeotropic or azeotrope-likecomposition of about 64.1 mole % HCl and 35.9 mole % PFC-116 is formedat 10 deg C. and 681 psia. Accordingly, the present invention providesan azeotropic or azeotrope-like composition consisting essentially offrom about 60.5 to about 64.1 mole % HCl and from about 39.5 to about35.9 mole % PFC-116, said composition having a boiling point of fromabout -60 deg C. at 80.6 psia to about 10 deg C. at 681 psia.

Referring now to FIG. 3, FIG. 3 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHCl and CFC-13 at -20 deg C., as indicated by a mixture of about 62.4mole % HCl and 37.6 mole % CFC-13 having the highest pressure over therange of compositions at this temperature. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like compositions ofabout 62.0 mole % HCl and 38.0 mole % CFC-13 is formed at -50 deg C. and101 psia and an azeotropic or azeotrope-like composition of about 61.9mole % HCl and 38.1 mole % CFC-13 is formed at 25 deg C. and 866 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 61.9 toabout 62.4 mole % HCl and from about 38.1 to about 37.6 mole % CFC-13,said composition having a boiling point of from about -50 deg C. at 101psia to about 25 deg C. at 866 psia.

Referring now to FIG. 4, FIG. 4 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHCl and HFC-23 at -20 deg C., as indicated by a mixture of about 56.9mole % HCl and 43.1 mole % HFC-23 having the highest pressure over therange of compositions at this temperature. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like compositions ofabout 59.2 mole % HCl and 40.8 mole % HFC-23 is formed at -50 deg C. and92.7 psia and an azeotropic or azeotrope-like composition of about 49.2mole % HCl and 50.8 mole % HFC-23 is formed at 25 deg C. and 866 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 59.2 toabout 49.2 mole % HCl and from about 40.8 to about 50.8 mole % HFC-23,said composition having a boiling point from about -50 deg C. at 93 psiato about 25 deg C. at 897 psia.

Referring now to FIG. 5, FIG. 5 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHCl and CFC-115 at -30 deg C., as indicated by a mixture of about 96.3mole % HCl and CFC-115 having the highest pressure over the range ofcompositions at this temperature. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like compositions of about95.0 mole % HCl and 5.0 mole % CFC-115 is formed at -50 deg C. and 75psia and an azeotropic or azeotrope-like composition of about 99.9 mole% HCl and 0.1 mole % CFC-115 is formed at 25 deg C. and 690 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 95 toabout 99.9 mole % HCl and from about 5 to about 0.1 mole % CFC-115, saidcomposition having a boiling point of from about -50 deg C. at 75 psiato about 25 deg C. at 690 psia.

Referring now to FIG. 6, FIG. 6 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHF and PFC-116 at -20 deg C., as indicated by mixtures of HF and PFC-116having a higher vapor pressure than either pure component at thistemperature, with the composition of the vapor space in the maximumpressure region being that of the azeotrope. Sampling of the vapor spaceand NRTL calculations show that the azeotropic or azeotrope-likecomposition was about 6.8 mole % HF and 93.2 mole % PFC-116 at thistemperature. Based upon these findings, it has been calculated that anazeotropic or azeotrope-like compositions of about 4.2 mole % HF and95.8 mole % PFC-116 is formed at -50 deg C. and 54.1 psia and anazeotropic or azeotrope-like composition of about 15.1 mole % HF and84.9 mole % PFC-116 is formed at 8 deg C. and 343 psia. Accordingly, thepresent invention provides an azeotropic or azeotrope-like compositionconsisting essentially of from about 4.2 to about 15.1 mole % HF andfrom about 95.8 to about 84.9 mole % PFC-116, said composition having aboiling point of from about -50 deg C. at 54 psia to about 8 deg C. at343 psia.

Referring now to FIG. 7, FIG. 7 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofCFC-13 and PFC-116 at -45.55 deg C., as indicated by a mixture of about23.2 mole % PFC-116 and 76.8 mole % CFC-13 having the highest pressureover the range of compositions at this temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 81.2 mole % CFC-13 and 18.8 mole % PFC-116 isformed at -60 deg C. and 41.3 psia and an azeotropic or azeotrope-likecomposition of about 53.4 mole % CFC-13 and 46.6 mole % PFC-116 isformed at 19 deg C. and 464 psia. Accordingly, the present inventionprovides an azeotropic or azeotrope-like composition consistingessentially of from about 18.8 to about 46.6 mole % PFC-116 and fromabout 81.2 to about 53.4 mole % CFC-13 and, said composition having aboiling point of from about -60 deg C. at 41.3 psia to about 19 deg C.at 464 psia.

Referring now to FIG. 8, FIG. 8 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHFC-23 and PFC-116 at -45.55 deg C., as indicated by a mixture of about60.2 mole % HFC-23 and 39.8 mole % PFC-116 having the highest pressureover the range of compositions at this temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 59.5 mole % HFC-23 and 40.5 mole % PFC-116 isformed at -60 deg C. and 58 psia and an azeotropic or azeotrope-likecomposition of about 65.8 mole % HFC-23 and 34.2 mole % PFC-116 isformed at 10 deg C. and 503 psia. Accordingly, the present inventionprovides an azeotropic or azeotrope-like composition Consistingessentially of from about 59.5 to about 65.8 mole % HFC-23 and fromabout 40.5 to about 34.2 mole % PFC-116, said composition having aboiling point of from about -60 deg C. at 58 psia to about 10 deg C. at503 psia.

Referring now to FIG. 9, FIG. 9 illustrates graphically the formation ofan azeotropic and azeotrope-like composition consisting essentially ofHFC-32 and PFC-116 at -19.6 deg C., as indicated by a mixture of about26.8 mole % HFC-32 and 73.2 mole % PFC-116 having the highest pressureover the range of compositions at this temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 18.3 mole % HFC-32 and 81.7 mole % PFC-116 isformed at -80 deg C. and 14.6 psia and an azeotropic or azeotrope-likecomposition of about 27.3 mole % HFC-32 and 72.7 mole % PFC-116 isformed at 10 deg C. and 412 psia. Accordingly, the present inventionprovides an azeotropic or azeotrope-like composition consistingessentially of from about 18.3 to about 26.8 mole % HFC-32 and fromabout 81.7 to about 73.2 mole % PFC-116, said composition having aboiling point of from about -80 deg C. at 14.6 psia to about 10 deg C.at 412 psia.

Referring now to FIG. 10, FIG. 10 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-115 at -20 deg C., as indicated by mixtures of HF andCFC-115 having a higher vapor pressure than either pure component atthis temperature, with the composition of the vapor space in the maximumpressure region being that of the azeotrope. Sampling of the vapor spaceand NRTL calculations showed that the azeotropic or azeotrope-likecomposition was about 25 mole % HF and 75 mole % CFC-115 at thistemperature. Based upon these findings, it has been calculated that anazeotropic or azeotrope-like compositions of about 17 mole % HF and 83mole % CFC-115 is formed at -60 deg C. and 5.5 psia and an azeotropic orazeotrope-like composition of about 24 mole % HF and 76 mole % CFC-115is formed at 50 deg C. and 287 psia. Accordingly, the present inventionprovides an azeotropic or azeotrope-like composition consistingessentially of from about 17 to about 24 mole % HF and from about 83 toabout 76 mole % CFC-115, said composition having a boiling point of fromabout -60 deg C. at 5.5 psia to about 50 deg C. at 287 psia.

Referring now to FIG. 11, FIG. 11 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-114 at -20 deg C., as indicated by mixtures of HF andCFC-114 having a higher vapor pressure than either pure component atthis temperature, with the composition of the vapor space in the maximumpressure region being that of the azeotrope at a specific temperatureand pressure. Sampling of the vapor space and NRTL calculations showedthat the azeotropic or azeotrope-like composition was about 67 mole % HFand 33 mole % CFC-114 at this temperature. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like compositions ofabout 68 mole % HF and 32 mole % CFC-114 is formed at -50 deg C. and 1.6psia and an azeotropic or azeotrope-like composition of about 50 mole %HF and 50 mole % CFC-114 is formed at 100 deg C. and 427 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 68 toabout 50 mole % HF and from about 32 to about 50 mole % CFC-114, saidcomposition having a boiling point of from about -50 deg C. at 1.6 psiato about 100 deg C. at 427 psia.

Referring now to FIG. 12, FIG. 12 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-114a at 20 deg C., as indicated by mixtures of HF andCFC-114a having a higher vapor pressure than either pure component atthis temperature, with the composition of the vapor space in the maximumpressure region being that of the azeotrope. Sampling of the vapor spaceand NRTL calculations showed that the azeotropic or azeotrope-likecomposition was about 63 mole % HF and 37 mole % CFC-114a at thistemperature. Based upon these findings, it has been calculated that anazeotropic or azeotrope-like compositions of about 65 mole % HF and 35mole % CFC-114a is formed at -25 deg C. and 6.8 psia and an azeotropicor azeotrope-like composition of about 57 mole % HF and 43 mole %CFC-114a is formed at 100 deg C. and 365 psia. Accordingly, the presentinvention provides an azeotropic or azeotrope-like compositionconsisting essentially of from about 65 to about 57 mole % HF and fromabout 35 to about 43 mole % CFC-114a, said composition having a boilingpoint of from about -25 deg C. at 6.8 psia to about 100 deg C. at 365psia.

Referring now to FIG. 13, FIG. 13 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-113 at -20 deg C., as indicated by specific molar mixturesof HF and CFC-113 having a higher vapor pressure than either purecomponent at this temperature, with the composition of the vapor spacein the maximum pressure region being that of the azeotrope. Sampling ofthe vapor space and NRTL calculations show that the azeotropic orazeotrope-like composition was about 93 mole % HF and 7 mole % CFC-113at this temperature. Based upon these findings, it has been calculatedthat an azeotropic or azeotrope-like compositions of about 94 mole % HFand 6 mole % CFC-113 is formed at -25 deg C. and 3 psia and anazeotropic or azeotrope-like composition of about 73 mole % HF and 27mole % CFC-113 is formed at 125 deg C. and 441 psia. Accordingly, thepresent invention provides an azeotropic or azeotrope-like compositionconsisting essentially of from about 73 to about 94 mole % HF and fromabout 27 to about 6 mole % CFC-113, said composition having a boilingpoint of from about -25 deg C. at 3 psia to about 125 deg C. at 441psia.

Referring now to FIG. 14, FIG. 14 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-113a at 20 deg C., as indicated by specific molar mixturesof HF and CFC-113a having a higher vapor pressure than either purecomponent at this temperature, with the composition of the vapor spacein the maximum pressure region being that of the azeotrope. Sampling ofthe vapor space and NRTL calculations show that the azeotropic orazeotrope-like composition was about 89 mole % HF and 11 mole CFC-113aat this temperature. Based upon these findings, it has been calculatedthat an azeotropic or azeotrope-like compositions of about 94 mole % HFand 6 mole % CFC-113a is formed at -25 deg C. and 3 psia and anazeotropic or azeotrope-like composition of about 70 mole % HF and 30mole % PFC-113a is formed at 125 deg C. and 455 psia. Accordingly, thepresent invention provides an azeotropic or azeotrope-like compositionconsisting essentially of from about 94 to about 70 mole % HF and fromabout 6 to about 30 mole % CFC-113a, said composition having a boilingpoint of from -25 deg C. at 3 psia to about 125 deg C. at 455 psia.

Referring now to FIG. 15, FIG. 15 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and HFC-125 at 20 deg C., as indicated by a mixture of about 14liquid mole % HF and 86 mole % HFC-125 having the highest pressure overthe range of compositions at this temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 11 mole % HF and 89 mole % PFC-125 is formed at-50 deg C. and 13.4 psia and an azeotropic or azeotrope-like compositionof about 15 mole % HF and 85 mole % HFC-125 is formed at 50 deg C. and388 psia. Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 14 toabout 15 mole % HF and from about 86 to about 85 mole % HFC-125, saidcomposition having a boiling point of from about -50 deg C. at 13.4 psiato about 50 deg C. at 388 psia.

Referring now to FIG. 16, FIG. 16 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and CFC-13 at -20 deg C., as indicated by a mixture of about 6mole % HF and 94 mole % CFC-13 having the highest pressure over therange of compositions at this temperature. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like compositions ofabout 3 mole % HF and 97 mole % CFC-13 is formed at -50 deg C. and 60psia and an azeotropic or azeotrope-like composition of about 11 mole %HF and 89 mole % CFC-13 is formed at 25 deg C. and 521 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 3 toabout 11 mole HF and from about 97 to about 89 mole % CFC-13, saidcomposition having a boiling point of from about -50 deg C. at 60 psiato about 25 deg C. at 521 psia.

Referring now to FIG. 17, FIG. 17 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and HCFC-22 at 70 deg C., as indicated by a mixture of about 9.9mole % HF and 90.1 mole % HCFC-22 having the highest vapor pressure overthe range of compositions at that temperature. Based upon thesefindings, it has been calculated that an azeotropic or azeotrope-likecompositions of about 14 mole % HF and 86 mole % HCFC-22 is formed at-50 deg C. and 10 psia and an azeotropic or azeotrope-like compositionof about 10 mole % HF and 90 mole % HCFC-22 is formed at 70 deg C. and458 psia. Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 14 toabout 10 mole % HF and from about 86 to about 90 mole % HCFC-22, saidcomposition having a boiling point of from about -50 deg C. at 10 psiato about 70 deg C. at 458 psia.

Referring now to FIG. 18, FIG. 18 illustrates graphically the formationof an azeotropic and azeotrope-like composition consisting essentiallyof HF and HFC-143a at 0 deg C., as indicated by a mixture of about 12.6mole % HF and 77.4 mole % HFC-143a having the highest pressure over therange of compositions at this temperature. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like compositions ofabout 13.8 mole % HF and 86.2 mole % PFC-143a is formed at -25 deg C.and 38.7 psia and an azeotropic or azeotrope-like composition of about 5mole % HF and 95 mole % HFC-143a is formed at 70 deg C. and 595 psia.Accordingly, the present invention provides an azeotropic orazeotrope-like composition consisting essentially of from about 13.8 toabout 5 mole % HF and from about 86.2 to about 95 mole % HFC-143a, saidcomposition having a boiling point of from about -25 deg C. at 38.7 psiato about 70 deg C. at 595 psia.

The followed is claimed:
 1. An azeotropic composition consistingessentially of about 95 to about 85 mole percent hexafluoroethane andabout 4 to about 15 mole percent hydrogen fluoride, said compositionhaving a boiling point from about -50 degrees C. at 54 psia to about 8degrees C. at 343 psia.
 2. An azeotropic composition consistingessentially of about 97 to about 89 mole percent chlorotrifluoroethaneand about 3 to about 11 mole percent hydrogen fluoride, said compositionhaving a boiling point from about -50 degrees C. at 60 psia to about 25degrees C. at 343 psia.
 3. A liquefied azeotropic composition consistingessentially of hexafluoroethane or chlorotrifluoromethane in combinationwith an effective amount of hydrogen fluoride to form said composition.4. An azeotropic composition consisting essentially of i)hexafluoroethane in combination with an effective amount of hydrogenfluoride to form said composition wherein said composition has a boilingpoint from about -50 degrees C. at about 54 psia to about 8 degrees C.at about 343 psia, or ii) chlorotrifluoromethane in combination with aneffective amount of hydrogen fluoride to form said composition whereinsaid composition has a boiling point from about -50 degrees C. at about60 psia to about 25 degrees C. at about 521 psia.
 5. A compositionconsisting essentially of hexafluoroethane or chlorotrifluoromethane andhydrogen fluoride wherein said composition has a boiling point fromabout -50 degrees C. at about 54 psia to about 8 degrees C. at about 343psia, or from about -50 degrees C. at about 60 psia to about 25 degreesC. at about 521 psia.
 6. The composition of claim 4 or 5 wherein theamount of hydrogen fluoride is from about 3 to about 15 mole percent. 7.The composition of claim 4 or 5 wherein the vapor pressure of thecomposition is greater than the vapor pressure of either purehexafluoroethane or hydrogen fluoride, or of eitherchlorotrifluoromethane or hydrogen fluoride.